diff --git a/test/built-ins/Array/15.4.5-1.js b/test/built-ins/Array/15.4.5-1.js
index 6eb1ae1271..59692ed6e6 100644
--- a/test/built-ins/Array/15.4.5-1.js
+++ b/test/built-ins/Array/15.4.5-1.js
@@ -9,4 +9,4 @@ description: Array instances have [[Class]] set to 'Array'
 var a = [];
 var s = Object.prototype.toString.call(a);
 
-assert.sameValue(s, '[object Array]', 's');
+assert.sameValue(s, '[object Array]', 'The value of s is expected to be "[object Array]"');
diff --git a/test/built-ins/Array/15.4.5.1-5-1.js b/test/built-ins/Array/15.4.5.1-5-1.js
index d92747a324..b0907e396d 100644
--- a/test/built-ins/Array/15.4.5.1-5-1.js
+++ b/test/built-ins/Array/15.4.5.1-5-1.js
@@ -11,4 +11,4 @@ description: >
 var a = [];
 a[4294967295] = "not an array element";
 
-assert.sameValue(a[4294967295], "not an array element", 'a[4294967295]');
+assert.sameValue(a[4294967295], "not an array element", 'The value of a[4294967295] is expected to be "not an array element"');
diff --git a/test/built-ins/Array/15.4.5.1-5-2.js b/test/built-ins/Array/15.4.5.1-5-2.js
index 27abd4c55b..8e60d6d8c6 100644
--- a/test/built-ins/Array/15.4.5.1-5-2.js
+++ b/test/built-ins/Array/15.4.5.1-5-2.js
@@ -11,4 +11,4 @@ description: >
 var a = [0, 1, 2];
 a[4294967295] = "not an array element";
 
-assert.sameValue(a.length, 3, 'a.length');
+assert.sameValue(a.length, 3, 'The value of a.length is expected to be 3');
diff --git a/test/built-ins/Array/S15.4.1_A1.1_T1.js b/test/built-ins/Array/S15.4.1_A1.1_T1.js
index e519a5f655..bb3cef639c 100644
--- a/test/built-ins/Array/S15.4.1_A1.1_T1.js
+++ b/test/built-ins/Array/S15.4.1_A1.1_T1.js
@@ -15,6 +15,10 @@ description: >
 //CHECK#1
 Array.prototype.myproperty = 42;
 var x = Array();
-assert.sameValue(x.myproperty, 42);
+assert.sameValue(x.myproperty, 42, 'The value of x.myproperty is expected to be 42');
 
-assert.sameValue(Object.prototype.hasOwnProperty.call(x, 'myproperty'), false);
+assert.sameValue(
+  Object.prototype.hasOwnProperty.call(x, 'myproperty'),
+  false,
+  'Object.prototype.hasOwnProperty.call(Array(), "myproperty") must return false'
+);
diff --git a/test/built-ins/Array/S15.4.1_A1.1_T2.js b/test/built-ins/Array/S15.4.1_A1.1_T2.js
index 7633f6587d..85cbc27b57 100644
--- a/test/built-ins/Array/S15.4.1_A1.1_T2.js
+++ b/test/built-ins/Array/S15.4.1_A1.1_T2.js
@@ -13,13 +13,9 @@ description: Array.prototype.toString = Object.prototype.toString
 //CHECK#1
 Array.prototype.toString = Object.prototype.toString;
 var x = Array();
-if (x.toString() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#1: Array.prototype.toString = Object.prototype.toString; var x = Array(); x.toString() === "[object " + "Array" + "]". Actual: ' + (x.toString()));
-}
+assert.sameValue(x.toString(), "[object Array]", 'x.toString() must return "[object Array]"');
 
 //CHECK#2
 Array.prototype.toString = Object.prototype.toString;
 var x = Array(0, 1, 2);
-if (x.toString() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#2: Array.prototype.toString = Object.prototype.toString; var x = Array(0,1,2); x.toString() === "[object " + "Array" + "]". Actual: ' + (x.toString()));
-}
+assert.sameValue(x.toString(), "[object Array]", 'x.toString() must return "[object Array]"');
diff --git a/test/built-ins/Array/S15.4.1_A1.1_T3.js b/test/built-ins/Array/S15.4.1_A1.1_T3.js
index cb586c8d46..21b852e671 100644
--- a/test/built-ins/Array/S15.4.1_A1.1_T3.js
+++ b/test/built-ins/Array/S15.4.1_A1.1_T3.js
@@ -10,7 +10,8 @@ es5id: 15.4.1_A1.1_T3
 description: Checking use isPrototypeOf
 ---*/
 
-//CHECK#1
-if (Array.prototype.isPrototypeOf(Array()) !== true) {
-  throw new Test262Error('#1: Array.prototype.isPrototypeOf(Array()) === true. Actual: ' + (Array.prototype.isPrototypeOf(Array())));
-}
+assert.sameValue(
+  Array.prototype.isPrototypeOf(Array()),
+  true,
+  'Array.prototype.isPrototypeOf(Array()) must return true'
+);
diff --git a/test/built-ins/Array/S15.4.1_A1.2_T1.js b/test/built-ins/Array/S15.4.1_A1.2_T1.js
index 5f28e62826..2cbe462f61 100644
--- a/test/built-ins/Array/S15.4.1_A1.2_T1.js
+++ b/test/built-ins/Array/S15.4.1_A1.2_T1.js
@@ -10,13 +10,9 @@ description: Checking use Object.prototype.toString
 //CHECK#1
 var x = Array();
 x.getClass = Object.prototype.toString;
-if (x.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#1: var x = Array(); x.getClass = Object.prototype.toString; x is Array object. Actual: ' + (x.getClass()));
-}
+assert.sameValue(x.getClass(), "[object Array]", 'x.getClass() must return "[object Array]"');
 
 //CHECK#2
 var x = Array(0, 1, 2);
 x.getClass = Object.prototype.toString;
-if (x.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#2: var x = Array(0,1,2); x.getClass = Object.prototype.toString; x is Array object. Actual: ' + (x.getClass()));
-}
+assert.sameValue(x.getClass(), "[object Array]", 'x.getClass() must return "[object Array]"');
diff --git a/test/built-ins/Array/S15.4.1_A1.3_T1.js b/test/built-ins/Array/S15.4.1_A1.3_T1.js
index 75d858da40..5f2a2d0027 100644
--- a/test/built-ins/Array/S15.4.1_A1.3_T1.js
+++ b/test/built-ins/Array/S15.4.1_A1.3_T1.js
@@ -11,12 +11,5 @@ description: Checking case when Array constructor is given one argument
 
 var x = Array(2);
 
-//CHECK#1
-if (x.length === 1) {
-  throw new Test262Error('#1: var x = Array(2); x.length !== 1');
-}
-
-//CHECK#2
-if (x[0] === 2) {
-  throw new Test262Error('#2: var x = Array(2); x[0] !== 2');
-}
+assert.notSameValue(x.length, 1, 'The value of x.length is not 1');
+assert.notSameValue(x[0], 2, 'The value of x[0] is not 2');
diff --git a/test/built-ins/Array/S15.4.1_A2.1_T1.js b/test/built-ins/Array/S15.4.1_A2.1_T1.js
index 223fa2fc98..80ac57fe06 100644
--- a/test/built-ins/Array/S15.4.1_A2.1_T1.js
+++ b/test/built-ins/Array/S15.4.1_A2.1_T1.js
@@ -8,18 +8,11 @@ info: |
 es5id: 15.4.1_A2.1_T1
 description: Array constructor is given no arguments or at least two arguments
 ---*/
+assert.sameValue(Array().length, 0, 'The value of Array().length is expected to be 0');
+assert.sameValue(Array(0, 1, 0, 1).length, 4, 'The value of Array(0, 1, 0, 1).length is expected to be 4');
 
-//CHECK#1
-if (Array().length !== 0) {
-  throw new Test262Error('#1: (Array().length === 0. Actual: ' + (Array().length));
-}
-
-//CHECK#2
-if (Array(0, 1, 0, 1).length !== 4) {
-  throw new Test262Error('#2: (Array(0,1,0,1).length === 4. Actual: ' + (Array(0, 1, 0, 1).length));
-}
-
-//CHECK#3
-if (Array(undefined, undefined).length !== 2) {
-  throw new Test262Error('#3: (Array(undefined, undefined).length === 2. Actual: ' + (Array(undefined, undefined).length));
-}
+assert.sameValue(
+  Array(undefined, undefined).length,
+  2,
+  'The value of Array(undefined, undefined).length is expected to be 2'
+);
diff --git a/test/built-ins/Array/S15.4.1_A2.2_T1.js b/test/built-ins/Array/S15.4.1_A2.2_T1.js
index 117e8592f4..f06603341f 100644
--- a/test/built-ins/Array/S15.4.1_A2.2_T1.js
+++ b/test/built-ins/Array/S15.4.1_A2.2_T1.js
@@ -33,6 +33,4 @@ for (var i = 0; i < 100; i++) {
   }
 }
 
-if (result !== true) {
-  throw new Test262Error('#1: x[i] === i. Actual: ' + (x[i]));
-}
+assert.sameValue(result, true, 'The value of result is expected to be true');
diff --git a/test/built-ins/Array/S15.4.1_A3.1_T1.js b/test/built-ins/Array/S15.4.1_A3.1_T1.js
index 50e47e7820..7405640e50 100644
--- a/test/built-ins/Array/S15.4.1_A3.1_T1.js
+++ b/test/built-ins/Array/S15.4.1_A3.1_T1.js
@@ -9,12 +9,10 @@ es5id: 15.4.1_A3.1_T1
 description: Checking use typeof, instanceof
 ---*/
 
-//CHECK#1
-if (typeof Array() !== "object") {
-  throw new Test262Error('#1: typeof Array() === "object". Actual: ' + (typeof Array()));
-}
+assert.sameValue(typeof Array(), "object", 'The value of `typeof Array()` is expected to be "object"');
 
-//CHECK#2
-if ((Array() instanceof Array) !== true) {
-  throw new Test262Error('#2: (Array() instanceof Array) === true. Actual: ' + (Array() instanceof Array));
-}
+assert.sameValue(
+  Array() instanceof Array,
+  true,
+  'The result of evaluating (Array() instanceof Array) is expected to be true'
+);
diff --git a/test/built-ins/Array/S15.4.2.1_A1.1_T1.js b/test/built-ins/Array/S15.4.2.1_A1.1_T1.js
index e1ff60ef62..0237a68c51 100644
--- a/test/built-ins/Array/S15.4.2.1_A1.1_T1.js
+++ b/test/built-ins/Array/S15.4.2.1_A1.1_T1.js
@@ -15,11 +15,5 @@ description: >
 //CHECK#1
 Array.prototype.myproperty = 1;
 var x = new Array();
-if (x.myproperty !== 1) {
-  throw new Test262Error('#1: Array.prototype.myproperty = 1; var x = new Array(); x.myproperty === 1. Actual: ' + (x.myproperty));
-}
-
-//CHECK#2
-if (x.hasOwnProperty('myproperty') !== false) {
-  throw new Test262Error('#2: Array.prototype.myproperty = 1; var x = new Array(); x.hasOwnProperty(\'myproperty\') === false. Actual: ' + (x.hasOwnProperty('myproperty')));
-}
+assert.sameValue(x.myproperty, 1, 'The value of x.myproperty is expected to be 1');
+assert.sameValue(x.hasOwnProperty('myproperty'), false, 'x.hasOwnProperty("myproperty") must return false');
diff --git a/test/built-ins/Array/S15.4.2.1_A1.1_T2.js b/test/built-ins/Array/S15.4.2.1_A1.1_T2.js
index 7ae477b065..61dff8e87f 100644
--- a/test/built-ins/Array/S15.4.2.1_A1.1_T2.js
+++ b/test/built-ins/Array/S15.4.2.1_A1.1_T2.js
@@ -13,13 +13,9 @@ description: Array.prototype.toString = Object.prototype.toString
 //CHECK#1
 Array.prototype.toString = Object.prototype.toString;
 var x = new Array();
-if (x.toString() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#1: Array.prototype.toString = Object.prototype.toString; var x = new Array(); x.toString() === "[object " + "Array" + "]". Actual: ' + (x.toString()));
-}
+assert.sameValue(x.toString(), "[object Array]", 'x.toString() must return "[object Array]"');
 
 //CHECK#2
 Array.prototype.toString = Object.prototype.toString;
 var x = new Array(0, 1, 2);
-if (x.toString() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#2: Array.prototype.toString = Object.prototype.toString; var x = new Array(0,1,2); x.toString() === "[object " + "Array" + "]". Actual: ' + (x.toString()));
-}
+assert.sameValue(x.toString(), "[object Array]", 'x.toString() must return "[object Array]"');
diff --git a/test/built-ins/Array/S15.4.2.1_A1.1_T3.js b/test/built-ins/Array/S15.4.2.1_A1.1_T3.js
index 9175ef79bc..3e6cb3cce0 100644
--- a/test/built-ins/Array/S15.4.2.1_A1.1_T3.js
+++ b/test/built-ins/Array/S15.4.2.1_A1.1_T3.js
@@ -9,8 +9,8 @@ info: |
 es5id: 15.4.2.1_A1.1_T3
 description: Checking use isPrototypeOf
 ---*/
-
-//CHECK#1
-if (Array.prototype.isPrototypeOf(new Array()) !== true) {
-  throw new Test262Error('#1: Array.prototype.isPrototypeOf(new Array()) === true. Actual: ' + (Array.prototype.isPrototypeOf(new Array())));
-}
+assert.sameValue(
+  Array.prototype.isPrototypeOf(new Array()),
+  true,
+  'Array.prototype.isPrototypeOf(new Array()) must return true'
+);
diff --git a/test/built-ins/Array/S15.4.2.1_A1.2_T1.js b/test/built-ins/Array/S15.4.2.1_A1.2_T1.js
index 3f9c18a715..a6f53cf277 100644
--- a/test/built-ins/Array/S15.4.2.1_A1.2_T1.js
+++ b/test/built-ins/Array/S15.4.2.1_A1.2_T1.js
@@ -10,13 +10,9 @@ description: Checking use Object.prototype.toString
 //CHECK#1
 var x = new Array();
 x.getClass = Object.prototype.toString;
-if (x.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#1: var x = new Array(); x.getClass = Object.prototype.toString; x is Array object. Actual: ' + (x.getClass()));
-}
+assert.sameValue(x.getClass(), "[object Array]", 'x.getClass() must return "[object Array]"');
 
 //CHECK#2
 var x = new Array(0, 1, 2);
 x.getClass = Object.prototype.toString;
-if (x.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#2: var x = new Array(0,1,2); x.getClass = Object.prototype.toString; x is Array object. Actual: ' + (x.getClass()));
-}
+assert.sameValue(x.getClass(), "[object Array]", 'x.getClass() must return "[object Array]"');
diff --git a/test/built-ins/Array/S15.4.2.1_A1.3_T1.js b/test/built-ins/Array/S15.4.2.1_A1.3_T1.js
index 673cfcb253..b34a497abd 100644
--- a/test/built-ins/Array/S15.4.2.1_A1.3_T1.js
+++ b/test/built-ins/Array/S15.4.2.1_A1.3_T1.js
@@ -11,12 +11,5 @@ description: Checking case when Array constructor is given one argument
 
 var x = new Array(2);
 
-//CHECK#1
-if (x.length === 1) {
-  throw new Test262Error('#1: var x = new Array(2); x.length !== 1');
-}
-
-//CHECK#2
-if (x[0] === 2) {
-  throw new Test262Error('#2: var x = new Array(2); x[0] !== 2');
-}
+assert.notSameValue(x.length, 1, 'The value of x.length is not 1');
+assert.notSameValue(x[0], 2, 'The value of x[0] is not 2');
diff --git a/test/built-ins/Array/S15.4.2.1_A2.1_T1.js b/test/built-ins/Array/S15.4.2.1_A2.1_T1.js
index 9c307a48ef..c245c96937 100644
--- a/test/built-ins/Array/S15.4.2.1_A2.1_T1.js
+++ b/test/built-ins/Array/S15.4.2.1_A2.1_T1.js
@@ -8,18 +8,11 @@ info: |
 es5id: 15.4.2.1_A2.1_T1
 description: Array constructor is given no arguments or at least two arguments
 ---*/
+assert.sameValue(new Array().length, 0, 'The value of new Array().length is expected to be 0');
+assert.sameValue(new Array(0, 1, 0, 1).length, 4, 'The value of new Array(0, 1, 0, 1).length is expected to be 4');
 
-//CHECK#1
-if (new Array().length !== 0) {
-  throw new Test262Error('#1: new Array().length === 0. Actual: ' + (new Array().length));
-}
-
-//CHECK#2
-if (new Array(0, 1, 0, 1).length !== 4) {
-  throw new Test262Error('#2: new Array(0,1,0,1).length === 4. Actual: ' + (new Array(0, 1, 0, 1).length));
-}
-
-//CHECK#3
-if (new Array(undefined, undefined).length !== 2) {
-  throw new Test262Error('#3: new Array(undefined, undefined).length === 2. Actual: ' + (new Array(undefined, undefined).length));
-}
+assert.sameValue(
+  new Array(undefined, undefined).length,
+  2,
+  'The value of new Array(undefined, undefined).length is expected to be 2'
+);
diff --git a/test/built-ins/Array/S15.4.2.1_A2.2_T1.js b/test/built-ins/Array/S15.4.2.1_A2.2_T1.js
index fa2726f068..3ee4c6f46d 100644
--- a/test/built-ins/Array/S15.4.2.1_A2.2_T1.js
+++ b/test/built-ins/Array/S15.4.2.1_A2.2_T1.js
@@ -33,6 +33,4 @@ for (var i = 0; i < 100; i++) {
   }
 }
 
-if (result !== true) {
-  throw new Test262Error('#1: x[i] === i. Actual: ' + (x[i]));
-}
+assert.sameValue(result, true, 'The value of result is expected to be true');
diff --git a/test/built-ins/Array/S15.4.3_A1.1_T1.js b/test/built-ins/Array/S15.4.3_A1.1_T1.js
index 79f6d795e9..eacde2d91a 100644
--- a/test/built-ins/Array/S15.4.3_A1.1_T1.js
+++ b/test/built-ins/Array/S15.4.3_A1.1_T1.js
@@ -13,12 +13,5 @@ description: >
 
 Function.prototype.myproperty = 1;
 
-//CHECK#1
-if (Array.myproperty !== 1) {
-  throw new Test262Error('#1: Function.prototype.myproperty = 1; Array.myproperty === 1. Actual: ' + (Array.myproperty));
-}
-
-//CHECK#2
-if (Array.hasOwnProperty('myproperty') !== false) {
-  throw new Test262Error('#2: Function.prototype.myproperty = 1; Array.hasOwnProperty(\'myproperty\') === false. Actual: ' + (Array.hasOwnProperty('myproperty')));
-}
+assert.sameValue(Array.myproperty, 1, 'The value of Array.myproperty is expected to be 1');
+assert.sameValue(Array.hasOwnProperty('myproperty'), false, 'Array.hasOwnProperty("myproperty") must return false');
diff --git a/test/built-ins/Array/S15.4.3_A1.1_T2.js b/test/built-ins/Array/S15.4.3_A1.1_T2.js
index 8fb6dae81d..3e5dfa605a 100644
--- a/test/built-ins/Array/S15.4.3_A1.1_T2.js
+++ b/test/built-ins/Array/S15.4.3_A1.1_T2.js
@@ -11,6 +11,9 @@ description: Function.prototype.toString = Object.prototype.toString
 
 //CHECK#1
 Function.prototype.toString = Object.prototype.toString;
-if (Array.toString() !== "[object " + "Function" + "]") {
-  throw new Test262Error('#1: Function.prototype.toString = Object.prototype.toString; Array.toString() === "[object " + "Function" + "]". Actual: ' + (Array.toString()));
-}
+
+assert.sameValue(
+  Array.toString(),
+  "[object Function]",
+  'Array.toString() must return "[object Function]"'
+);
diff --git a/test/built-ins/Array/S15.4.3_A1.1_T3.js b/test/built-ins/Array/S15.4.3_A1.1_T3.js
index 03fcf9244d..a51e1001cf 100644
--- a/test/built-ins/Array/S15.4.3_A1.1_T3.js
+++ b/test/built-ins/Array/S15.4.3_A1.1_T3.js
@@ -8,8 +8,8 @@ info: |
 es5id: 15.4.3_A1.1_T3
 description: Checking use isPrototypeOf
 ---*/
-
-//CHECK#1
-if (Function.prototype.isPrototypeOf(Array) !== true) {
-  throw new Test262Error('#1: Function.prototype.isPrototypeOf(Array) === true. Actual: ' + (Function.prototype.isPrototypeOf(Array)));
-}
+assert.sameValue(
+  Function.prototype.isPrototypeOf(Array),
+  true,
+  'Function.prototype.isPrototypeOf(Array) must return true'
+);
diff --git a/test/built-ins/Array/S15.4.5.1_A1.2_T2.js b/test/built-ins/Array/S15.4.5.1_A1.2_T2.js
index c8c4dd7d57..b0c43932d8 100644
--- a/test/built-ins/Array/S15.4.5.1_A1.2_T2.js
+++ b/test/built-ins/Array/S15.4.5.1_A1.2_T2.js
@@ -14,12 +14,8 @@ description: Checking an inherited property
 //CHECK#1
 Array.prototype[2] = -1;
 var x = [0, 1, 2];
-if (x[2] !== 2) {
-  throw new Test262Error('#1: Array.prototype[2] = -1; x = [0,1,3]; x[2] === 2. Actual: ' + (x[2]));
-}
+assert.sameValue(x[2], 2, 'The value of x[2] is expected to be 2');
 
 //CHECK#2
 x.length = 2;
-if (x[2] !== -1) {
-  throw new Test262Error('#2: Array.prototype[2] = -1; x = [0,1,3]; x.length = 2; x[2] === -1. Actual: ' + (x[2]));
-}
+assert.sameValue(x[2], -1, 'The value of x[2] is expected to be -1');
diff --git a/test/built-ins/Array/S15.4.5.1_A2.1_T1.js b/test/built-ins/Array/S15.4.5.1_A2.1_T1.js
index dd67a6ce22..720470d820 100644
--- a/test/built-ins/Array/S15.4.5.1_A2.1_T1.js
+++ b/test/built-ins/Array/S15.4.5.1_A2.1_T1.js
@@ -12,32 +12,17 @@ description: P in [4294967295, -1, true]
 //CHECK#1
 var x = [];
 x[4294967295] = 1;
-if (x.length !== 0) {
-  throw new Test262Error('#1.1: x = []; x[4294967295] = 1; x.length === 0. Actual: ' + (x.length));
-}
-
-if (x[4294967295] !== 1) {
-  throw new Test262Error('#1.2: x = []; x[4294967295] = 1; x[4294967295] === 1. Actual: ' + (x[4294967295]));
-}
+assert.sameValue(x.length, 0, 'The value of x.length is expected to be 0');
+assert.sameValue(x[4294967295], 1, 'The value of x[4294967295] is expected to be 1');
 
 //CHECK#2
 x = [];
 x[-1] = 1;
-if (x.length !== 0) {
-  throw new Test262Error('#2.1: x = []; x[-1] = 1; x.length === 0. Actual: ' + (x.length));
-}
-
-if (x[-1] !== 1) {
-  throw new Test262Error('#2.2: x = []; x[-1] = 1; x[-1] === 1. Actual: ' + (x[-1]));
-}
+assert.sameValue(x.length, 0, 'The value of x.length is expected to be 0');
+assert.sameValue(x[-1], 1, 'The value of x[-1] is expected to be 1');
 
 //CHECK#3
 x = [];
 x[true] = 1;
-if (x.length !== 0) {
-  throw new Test262Error('#3.1: x = []; x[true] = 1; x.length === 0. Actual: ' + (x.length));
-}
-
-if (x[true] !== 1) {
-  throw new Test262Error('#3.2: x = []; x[true] = 1; x[true] === 1. Actual: ' + (x[true]));
-}
+assert.sameValue(x.length, 0, 'The value of x.length is expected to be 0');
+assert.sameValue(x[true], 1, 'The value of x[true] is expected to be 1');
diff --git a/test/built-ins/Array/S15.4.5.1_A2.2_T1.js b/test/built-ins/Array/S15.4.5.1_A2.2_T1.js
index d0668db59e..9df4c565e8 100644
--- a/test/built-ins/Array/S15.4.5.1_A2.2_T1.js
+++ b/test/built-ins/Array/S15.4.5.1_A2.2_T1.js
@@ -12,18 +12,12 @@ description: length === 100, P in [0, 98, 99]
 //CHECK#1
 var x = Array(100);
 x[0] = 1;
-if (x.length !== 100) {
-  throw new Test262Error('#1: x = Array(100); x[0] = 1; x.length === 100. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 100, 'The value of x.length is expected to be 100');
 
 //CHECK#2
 x[98] = 1;
-if (x.length !== 100) {
-  throw new Test262Error('#2: x = Array(100); x[0] = 1; x[98] = 1; x.length === 100. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 100, 'The value of x.length is expected to be 100');
 
 //CHECK#3
 x[99] = 1;
-if (x.length !== 100) {
-  throw new Test262Error('#3: x = Array(100); x[0] = 1; x[98] = 1; x[99] = 1; x.length === 100. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 100, 'The value of x.length is expected to be 100');
diff --git a/test/built-ins/Array/S15.4.5.1_A2.3_T1.js b/test/built-ins/Array/S15.4.5.1_A2.3_T1.js
index 8a88a56b84..35a69e56de 100644
--- a/test/built-ins/Array/S15.4.5.1_A2.3_T1.js
+++ b/test/built-ins/Array/S15.4.5.1_A2.3_T1.js
@@ -12,12 +12,8 @@ description: length = 100, P in [100, 199]
 //CHECK#1
 var x = Array(100);
 x[100] = 1;
-if (x.length !== 101) {
-  throw new Test262Error('#1: x = Array(100); x[100] = 1; x.length === 101. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 101, 'The value of x.length is expected to be 101');
 
 //CHECK#2
 x[199] = 1;
-if (x.length !== 200) {
-  throw new Test262Error('#2: x = Array(100); x[100] = 1; x[199] = 1; x.length === 100. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 200, 'The value of x.length is expected to be 200');
diff --git a/test/built-ins/Array/S15.4.5.2_A1_T1.js b/test/built-ins/Array/S15.4.5.2_A1_T1.js
index 38611b7729..a8fc10e8bf 100644
--- a/test/built-ins/Array/S15.4.5.2_A1_T1.js
+++ b/test/built-ins/Array/S15.4.5.2_A1_T1.js
@@ -12,30 +12,20 @@ description: Checking boundary points
 
 //CHECK#1
 var x = [];
-if (x.length !== 0) {
-  throw new Test262Error('#1: x = []; x.length === 0. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 0, 'The value of x.length is expected to be 0');
 
 //CHECK#2
 x[0] = 1;
-if (x.length !== 1) {
-  throw new Test262Error('#2: x = []; x[1] = 1; x.length === 1. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
 
 //CHECK#3
 x[1] = 1;
-if (x.length !== 2) {
-  throw new Test262Error('#3: x = []; x[0] = 1; x[1] = 1; x.length === 2. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 2, 'The value of x.length is expected to be 2');
 
 //CHECK#4
 x[2147483648] = 1;
-if (x.length !== 2147483649) {
-  throw new Test262Error('#4: x = []; x[0] = 1; x[1] = 1; x[2147483648] = 1; x.length === 2147483649. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 2147483649, 'The value of x.length is expected to be 2147483649');
 
 //CHECK#5
 x[4294967294] = 1;
-if (x.length !== 4294967295) {
-  throw new Test262Error('#5: x = []; x[0] = 1; x[1] = 1; x[2147483648] = 1; x[42949672954] = 1; x.length === 4294967295. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 4294967295, 'The value of x.length is expected to be 4294967295');
diff --git a/test/built-ins/Array/S15.4.5.2_A1_T2.js b/test/built-ins/Array/S15.4.5.2_A1_T2.js
index b558c661ec..0666c2f830 100644
--- a/test/built-ins/Array/S15.4.5.2_A1_T2.js
+++ b/test/built-ins/Array/S15.4.5.2_A1_T2.js
@@ -13,14 +13,10 @@ description: P = "2^32 - 1" is not index array
 //CHECK#1
 var x = [];
 x[4294967295] = 1;
-if (x.length !== 0) {
-  throw new Test262Error('#1: x = []; x[4294967295] = 1; x.length === 0. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 0, 'The value of x.length is expected to be 0');
 
 //CHECK#2
 var y = [];
 y[1] = 1;
 y[4294967295] = 1;
-if (y.length !== 2) {
-  throw new Test262Error('#2: y = []; y[1] = 1; y[4294967295] = 1; y.length === 2. Actual: ' + (y.length));
-}
+assert.sameValue(y.length, 2, 'The value of y.length is expected to be 2');
diff --git a/test/built-ins/Array/S15.4.5.2_A2_T1.js b/test/built-ins/Array/S15.4.5.2_A2_T1.js
index 6a8ae1ec57..81c2b7b837 100644
--- a/test/built-ins/Array/S15.4.5.2_A2_T1.js
+++ b/test/built-ins/Array/S15.4.5.2_A2_T1.js
@@ -11,24 +11,16 @@ description: Checking length property
 
 //CHECK#1
 var x = [];
-if (x.length !== 0) {
-  throw new Test262Error('#1: x = []; x.length === 0. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 0, 'The value of x.length is expected to be 0');
 
 //CHECK#2
 x[0] = 1;
-if (x.length !== 1) {
-  throw new Test262Error('#2: x = []; x[1] = 1; x.length === 1. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
 
 //CHECK#3
 x[1] = 1;
-if (x.length !== 2) {
-  throw new Test262Error('#3: x = []; x[0] = 1; x[1] = 1; x.length === 2. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 2, 'The value of x.length is expected to be 2');
 
 //CHECK#4
 x[9] = 1;
-if (x.length !== 10) {
-  throw new Test262Error('#4: x = []; x[0] = 1; x[1] = 1; x[9] = 1; x.length === 10. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 10, 'The value of x.length is expected to be 10');
diff --git a/test/built-ins/Array/S15.4.5.2_A3_T1.js b/test/built-ins/Array/S15.4.5.2_A3_T1.js
index 05988eda66..703c074ba2 100644
--- a/test/built-ins/Array/S15.4.5.2_A3_T1.js
+++ b/test/built-ins/Array/S15.4.5.2_A3_T1.js
@@ -14,18 +14,10 @@ description: >
 //CHECK#1
 var x = [];
 x.length = 1;
-if (x.length !== 1) {
-  throw new Test262Error('#1: x = []; x.length = 1; x.length === 1. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
 
 //CHECK#2
 x[5] = 1;
 x.length = 10;
-if (x.length !== 10) {
-  throw new Test262Error('#2: x = []; x.length = 1; x[5] = 1; x.length = 10; x.length === 10. Actual: ' + (x.length));
-}
-
-//CHECK#3
-if (x[5] !== 1) {
-  throw new Test262Error('#3: x = []; x.length = 1; x[5] = 1; x.length = 10; x[5] = 1');
-}
+assert.sameValue(x.length, 10, 'The value of x.length is expected to be 10');
+assert.sameValue(x[5], 1, 'The value of x[5] is expected to be 1');
diff --git a/test/built-ins/Array/S15.4.5.2_A3_T2.js b/test/built-ins/Array/S15.4.5.2_A3_T2.js
index 87312de88e..c71f8abc9c 100644
--- a/test/built-ins/Array/S15.4.5.2_A3_T2.js
+++ b/test/built-ins/Array/S15.4.5.2_A3_T2.js
@@ -17,34 +17,18 @@ x[1] = 1;
 x[3] = 3;
 x[5] = 5;
 x.length = 4;
-if (x.length !== 4) {
-  throw new Test262Error('#1: x = []; x[1] = 1; x[3] = 3; x[5] = 5; x.length = 4; x.length === 4. Actual: ' + (x.length));
-}
-
-//CHECK#2
-if (x[5] !== undefined) {
-  throw new Test262Error('#2: x = []; x[1] = 1; x[3] = 3; x[5] = 5; x.length = 4; x[5] === undefined. Actual: ' + (x[5]));
-}
-
-//CHECK#3
-if (x[3] !== 3) {
-  throw new Test262Error('#3: x = []; x[1] = 1; x[3] = 3; x[5] = 5; x.length = 4; x[3] === 3. Actual: ' + (x[3]));
-}
+assert.sameValue(x.length, 4, 'The value of x.length is expected to be 4');
+assert.sameValue(x[5], undefined, 'The value of x[5] is expected to equal undefined');
+assert.sameValue(x[3], 3, 'The value of x[3] is expected to be 3');
 
 //CHECK#4
 x.length = new Number(6);
-if (x[5] !== undefined) {
-  throw new Test262Error('#4: x = []; x[1] = 1; x[3] = 3; x[5] = 5; x.length = 4; x.length = new Number(6); x[5] === undefined. Actual: ' + (x[5]));
-}
+assert.sameValue(x[5], undefined, 'The value of x[5] is expected to equal undefined');
 
 //CHECK#5
 x.length = 0;
-if (x[0] !== undefined) {
-  throw new Test262Error('#5: x = []; x[1] = 1; x[3] = 3; x[5] = 5; x.length = 4; x.length = new Number(6); x.length = 0; x[0] === undefined. Actual: ' + (x[0]));
-}
+assert.sameValue(x[0], undefined, 'The value of x[0] is expected to equal undefined');
 
 //CHECK#6
 x.length = 1;
-if (x[1] !== undefined) {
-  throw new Test262Error('#6: x = []; x[1] = 1; x[3] = 3; x[5] = 5; x.length = 4; x.length = new Number(6); x.length = 0; x.length = 1; x[1] === undefined. Actual: ' + (x[1]));
-}
+assert.sameValue(x[1], undefined, 'The value of x[1] is expected to equal undefined');
diff --git a/test/built-ins/Array/S15.4.5.2_A3_T3.js b/test/built-ins/Array/S15.4.5.2_A3_T3.js
index f7bce716ce..eb7d7ea67c 100644
--- a/test/built-ins/Array/S15.4.5.2_A3_T3.js
+++ b/test/built-ins/Array/S15.4.5.2_A3_T3.js
@@ -12,9 +12,7 @@ description: "[[Put]] (length, 4294967296)"
 //CHECK#1
 var x = [];
 x.length = 4294967295;
-if (x.length !== 4294967295) {
-  throw new Test262Error('#1: x = []; x.length = 4294967295; x.length === 4294967295');
-}
+assert.sameValue(x.length, 4294967295, 'The value of x.length is expected to be 4294967295');
 
 //CHECK#2
 try {
@@ -22,7 +20,9 @@ try {
   x.length = 4294967296;
   throw new Test262Error('#2.1: x = []; x.length = 4294967296 throw RangeError. Actual: x.length === ' + (x.length));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#2.2: x = []; x.length = 4294967296 throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
diff --git a/test/built-ins/Array/S15.4_A1.1_T10.js b/test/built-ins/Array/S15.4_A1.1_T10.js
index ac32381804..521828b54b 100644
--- a/test/built-ins/Array/S15.4_A1.1_T10.js
+++ b/test/built-ins/Array/S15.4_A1.1_T10.js
@@ -20,7 +20,5 @@ for (var i = 0; i < 32; i++) {
 k = 1;
 for (i = 0; i < 32; i++) {
   k = k * 2;
-  if (x[k - 2] !== k) {
-    throw new Test262Error('#' + (k - 2) + ': ');
-  }
+  assert.sameValue(x[k - 2], k, 'The value of x[k - 2] is expected to equal the value of k');
 }
diff --git a/test/built-ins/Array/S15.4_A1.1_T4.js b/test/built-ins/Array/S15.4_A1.1_T4.js
index d5aa1b1fb2..efa4fe7d2b 100644
--- a/test/built-ins/Array/S15.4_A1.1_T4.js
+++ b/test/built-ins/Array/S15.4_A1.1_T4.js
@@ -12,13 +12,9 @@ description: Checking for string primitive
 //CHECK#1
 var x = [];
 x["0"] = 0;
-if (x[0] !== 0) {
-  throw new Test262Error('#1: x = []; x["0"] = 0; x[0] === 0. Actual: ' + (x[0]));
-}
+assert.sameValue(x[0], 0, 'The value of x[0] is expected to be 0');
 
 //CHECK#2
 var y = [];
 y["1"] = 1;
-if (y[1] !== 1) {
-  throw new Test262Error('#2: y = []; y["1"] = 1; y[1] === 1. Actual: ' + (y[1]));
-}
+assert.sameValue(y[1], 1, 'The value of y[1] is expected to be 1');
diff --git a/test/built-ins/Array/S15.4_A1.1_T5.js b/test/built-ins/Array/S15.4_A1.1_T5.js
index e5c2961fce..73ca7f35f6 100644
--- a/test/built-ins/Array/S15.4_A1.1_T5.js
+++ b/test/built-ins/Array/S15.4_A1.1_T5.js
@@ -12,23 +12,11 @@ description: Checking for null and undefined
 //CHECK#1
 var x = [];
 x[null] = 0;
-if (x[0] !== undefined) {
-  throw new Test262Error('#1: x = []; x[null] = 1; x[0] === undefined. Actual: ' + (x[0]));
-}
-
-//CHECK#2
-if (x["null"] !== 0) {
-  throw new Test262Error('#2: x = []; x[null] = 1; x["null"] === 0. Actual: ' + (x["null"]));
-}
+assert.sameValue(x[0], undefined, 'The value of x[0] is expected to equal undefined');
+assert.sameValue(x["null"], 0, 'The value of x["null"] is expected to be 0');
 
 //CHECK#3
 var y = [];
 y[undefined] = 0;
-if (y[0] !== undefined) {
-  throw new Test262Error('#3: y = []; y[undefined] = 0; y[0] === undefined. Actual: ' + (y[0]));
-}
-
-//CHECK#4
-if (y["undefined"] !== 0) {
-  throw new Test262Error('#4: y = []; y[undefined] = 1; y["undefined"] === 0. Actual: ' + (y["undefined"]));
-}
+assert.sameValue(y[0], undefined, 'The value of y[0] is expected to equal undefined');
+assert.sameValue(y["undefined"], 0, 'The value of y["undefined"] is expected to be 0');
diff --git a/test/built-ins/Array/S15.4_A1.1_T6.js b/test/built-ins/Array/S15.4_A1.1_T6.js
index 009cc79727..0c6facf162 100644
--- a/test/built-ins/Array/S15.4_A1.1_T6.js
+++ b/test/built-ins/Array/S15.4_A1.1_T6.js
@@ -12,22 +12,10 @@ description: Checking for Boolean object
 //CHECK#1
 var x = [];
 x[new Boolean(true)] = 1;
-if (x[1] !== undefined) {
-  throw new Test262Error('#1: x = []; x[new Boolean(true)] = 1; x[1] === undefined. Actual: ' + (x[1]));
-}
-
-//CHECK#2
-if (x["true"] !== 1) {
-  throw new Test262Error('#2: x = []; x[true] = 1; x["true"] === 1. Actual: ' + (x["true"]));
-}
+assert.sameValue(x[1], undefined, 'The value of x[1] is expected to equal undefined');
+assert.sameValue(x["true"], 1, 'The value of x["true"] is expected to be 1');
 
 //CHECK#3
 x[new Boolean(false)] = 0;
-if (x[0] !== undefined) {
-  throw new Test262Error('#3: x = []; x[true] = 1; x[new Boolean(false)] = 0; x[0] === undefined. Actual: ' + (x[0]));
-}
-
-//CHECK#4
-if (x["false"] !== 0) {
-  throw new Test262Error('#4: x = []; x[false] = 1; x["false"] === 0. Actual: ' + (x["false"]));
-}
+assert.sameValue(x[0], undefined, 'The value of x[0] is expected to equal undefined');
+assert.sameValue(x["false"], 0, 'The value of x["false"] is expected to be 0');
diff --git a/test/built-ins/Array/S15.4_A1.1_T7.js b/test/built-ins/Array/S15.4_A1.1_T7.js
index 1732a5912f..011a5deeb9 100644
--- a/test/built-ins/Array/S15.4_A1.1_T7.js
+++ b/test/built-ins/Array/S15.4_A1.1_T7.js
@@ -12,20 +12,14 @@ description: Checking for Number object
 //CHECK#1
 var x = [];
 x[new Number(0)] = 0;
-if (x[0] !== 0) {
-  throw new Test262Error('#1: x = []; x[new Number(0)] = 0; x[0] === 0. Actual: ' + (x[0]));
-}
+assert.sameValue(x[0], 0, 'The value of x[0] is expected to be 0');
 
 //CHECK#2
 var y = [];
 y[new Number(1)] = 1;
-if (y[1] !== 1) {
-  throw new Test262Error('#2: y = []; y[new Number(1)] = 1; y[1] === 1. Actual: ' + (y[1]));
-}
+assert.sameValue(y[1], 1, 'The value of y[1] is expected to be 1');
 
 //CHECK#3
 var z = [];
 z[new Number(1.1)] = 1;
-if (z["1.1"] !== 1) {
-  throw new Test262Error('#3: z = []; z[new Number(1.1)] = 1; z["1.1"] === 1. Actual: ' + (z["1.1"]));
-}
+assert.sameValue(z["1.1"], 1, 'The value of z["1.1"] is expected to be 1');
diff --git a/test/built-ins/Array/S15.4_A1.1_T8.js b/test/built-ins/Array/S15.4_A1.1_T8.js
index c8f2ccb716..927ba0e72d 100644
--- a/test/built-ins/Array/S15.4_A1.1_T8.js
+++ b/test/built-ins/Array/S15.4_A1.1_T8.js
@@ -12,20 +12,14 @@ description: Checking for Number object
 //CHECK#1
 var x = [];
 x[new String("0")] = 0;
-if (x[0] !== 0) {
-  throw new Test262Error('#1: x = []; x[new String("0")] = 0; x[0] === 0. Actual: ' + (x[0]));
-}
+assert.sameValue(x[0], 0, 'The value of x[0] is expected to be 0');
 
 //CHECK#2
 var y = [];
 y[new String("1")] = 1;
-if (y[1] !== 1) {
-  throw new Test262Error('#2: y = []; y[new String("1")] = 1; y[1] === 1. Actual: ' + (y[1]));
-}
+assert.sameValue(y[1], 1, 'The value of y[1] is expected to be 1');
 
 //CHECK#3
 var z = [];
 z[new String("1.1")] = 1;
-if (z["1.1"] !== 1) {
-  throw new Test262Error('#3: z = []; z[new String("1.1")] = 1; z["1.1"] === 1. Actual: ' + (z["1.1"]));
-}
+assert.sameValue(z["1.1"], 1, 'The value of z["1.1"] is expected to be 1');
diff --git a/test/built-ins/Array/S15.4_A1.1_T9.js b/test/built-ins/Array/S15.4_A1.1_T9.js
index 1e62315a20..ed65434240 100644
--- a/test/built-ins/Array/S15.4_A1.1_T9.js
+++ b/test/built-ins/Array/S15.4_A1.1_T9.js
@@ -17,9 +17,7 @@ var object = {
   }
 };
 x[object] = 0;
-if (x["[object Object]"] !== 0) {
-  throw new Test262Error('#1: x = []; var object = {valueOf: function() {return 1}}; x[object] = 0; x["[object Object]"] === 0. Actual: ' + (x["[object Object]"]));
-}
+assert.sameValue(x["[object Object]"], 0, 'The value of x["[object Object]"] is expected to be 0');
 
 //CHECK#2
 x = [];
@@ -32,9 +30,7 @@ var object = {
   }
 };
 x[object] = 0;
-if (x[0] !== 0) {
-  throw new Test262Error('#2: x = []; var object = {valueOf: function() {return 1}, toString: function() {return 0}}; x[object] = 0; x[0] === 0. Actual: ' + (x[0]));
-}
+assert.sameValue(x[0], 0, 'The value of x[0] is expected to be 0');
 
 //CHECK#3
 x = [];
@@ -47,9 +43,7 @@ var object = {
   }
 };
 x[object] = 0;
-if (x[1] !== 0) {
-  throw new Test262Error('#3: x = []; var object = {valueOf: function() {return 1}, toString: function() {return {}}}; x[object] = 0; x[1] === 0. Actual: ' + (x[1]));
-}
+assert.sameValue(x[1], 0, 'The value of x[1] is expected to be 0');
 
 //CHECK#4
 try {
@@ -63,16 +57,10 @@ try {
     }
   };
   x[object] = 0;
-  if (x[1] !== 0) {
-    throw new Test262Error('#4.1: x = []; var object = {valueOf: function() {throw "error"}, toString: function() {return 1}}; x[object] = 0; x[1] === 1. Actual: ' + (x[1]));
-  }
+  assert.sameValue(x[1], 0, 'The value of x[1] is expected to be 0');
 }
 catch (e) {
-  if (e === "error") {
-    throw new Test262Error('#4.2: x = []; var object = {valueOf: function() {throw "error"}, toString: function() {return 1}}; x[object] = 0; x[1] === 1. Actual: ' + ("error"));
-  } else {
-    throw new Test262Error('#4.3: x = []; var object = {valueOf: function() {throw "error"}, toString: function() {return 1}}; x[object] = 0; x[1] === 1. Actual: ' + (e));
-  }
+  assert.notSameValue(e, "error", 'The value of e is not "error"');
 }
 
 //CHECK#5
@@ -83,9 +71,7 @@ var object = {
   }
 };
 x[object] = 0;
-if (x[1] !== 0) {
-  throw new Test262Error('#5: x = []; var object = {toString: function() {return 1}}; x[object] = 0; x[1] === 0. Actual: ' + (x[1]));
-}
+assert.sameValue(x[1], 0, 'The value of x[1] is expected to be 0');
 
 //CHECK#6
 x = [];
@@ -98,9 +84,7 @@ var object = {
   }
 }
 x[object] = 0;
-if (x[1] !== 0) {
-  throw new Test262Error('#6: x = []; var object = {valueOf: function() {return {}}, toString: function() {return 1}}; x[object] = 0; x[1] === 0. Actual: ' + (x[1]));
-}
+assert.sameValue(x[1], 0, 'The value of x[1] is expected to be 0');
 
 //CHECK#7
 try {
@@ -117,9 +101,7 @@ try {
   throw new Test262Error('#7.1: x = []; var object = {valueOf: function() {return 1}, toString: function() {throw "error"}}; x[object] throw "error". Actual: ' + (x[object]));
 }
 catch (e) {
-  if (e !== "error") {
-    throw new Test262Error('#7.2: x = []; var object = {valueOf: function() {return 1}, toString: function() {throw "error"}}; x[object] throw "error". Actual: ' + (e));
-  }
+  assert.sameValue(e, "error", 'The value of e is expected to be "error"');
 }
 
 //CHECK#8
@@ -137,7 +119,9 @@ try {
   throw new Test262Error('#8.1: x = []; var object = {valueOf: function() {return {}}, toString: function() {return {}}}; x[object] throw TypeError. Actual: ' + (x[object]));
 }
 catch (e) {
-  if ((e instanceof TypeError) !== true) {
-    throw new Test262Error('#8.2: x = []; var object = {valueOf: function() {return {}}, toString: function() {return {}}}; x[object] throw TypeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof TypeError,
+    true,
+    'The result of evaluating (e instanceof TypeError) is expected to be true'
+  );
 }
diff --git a/test/built-ins/Array/constructor.js b/test/built-ins/Array/constructor.js
index 5ee0bd0201..e9d3222b7b 100644
--- a/test/built-ins/Array/constructor.js
+++ b/test/built-ins/Array/constructor.js
@@ -7,4 +7,4 @@ description: >
   The Array constructor is a built-in function
 ---*/
 
-assert.sameValue(typeof Array, 'function');
+assert.sameValue(typeof Array, 'function', 'The value of `typeof Array` is expected to be "function"');
diff --git a/test/built-ins/Array/from/Array.from-name.js b/test/built-ins/Array/from/Array.from-name.js
index ff6f4913af..75795bd73d 100644
--- a/test/built-ins/Array/from/Array.from-name.js
+++ b/test/built-ins/Array/from/Array.from-name.js
@@ -22,7 +22,7 @@ includes: [propertyHelper.js]
 assert.sameValue(
   Array.from.name,
   'from',
-  'The value of `Array.from.name` is `"from"`'
+  'The value of Array.from.name is expected to be "from"'
 );
 
 verifyNotEnumerable(Array.from, 'name');
diff --git a/test/built-ins/Array/from/Array.from_arity.js b/test/built-ins/Array/from/Array.from_arity.js
index 88eb713f0e..2aa04a0ebd 100644
--- a/test/built-ins/Array/from/Array.from_arity.js
+++ b/test/built-ins/Array/from/Array.from_arity.js
@@ -14,7 +14,7 @@ info: |
 includes: [propertyHelper.js]
 ---*/
 
-assert.sameValue(Array.from.length, 1);
+assert.sameValue(Array.from.length, 1, 'The value of Array.from.length is expected to be 1');
 
 verifyNotEnumerable(Array.from, 'length');
 verifyNotWritable(Array.from, 'length');
diff --git a/test/built-ins/Array/from/Array.from_forwards-length-for-array-likes.js b/test/built-ins/Array/from/Array.from_forwards-length-for-array-likes.js
index 382d6fab0f..ec5bf2063e 100644
--- a/test/built-ins/Array/from/Array.from_forwards-length-for-array-likes.js
+++ b/test/built-ins/Array/from/Array.from_forwards-length-for-array-likes.js
@@ -31,6 +31,9 @@ result = Array.from.call(MyCollection, {
   length: 42
 });
 
-assert.sameValue(result.args.length, 1);
-assert.sameValue(result.args[0], 42);
-assert(result instanceof MyCollection);
+assert.sameValue(result.args.length, 1, 'The value of result.args.length is expected to be 1');
+assert.sameValue(result.args[0], 42, 'The value of result.args[0] is expected to be 42');
+assert(
+  result instanceof MyCollection,
+  'The result of evaluating (result instanceof MyCollection) is expected to be true'
+);
diff --git a/test/built-ins/Array/from/calling-from-valid-1-noStrict.js b/test/built-ins/Array/from/calling-from-valid-1-noStrict.js
index 72d7139765..35dc3e0ed4 100644
--- a/test/built-ins/Array/from/calling-from-valid-1-noStrict.js
+++ b/test/built-ins/Array/from/calling-from-valid-1-noStrict.js
@@ -43,24 +43,24 @@ function mapFn(value) {
 
 var result = Array.from(list, mapFn);
 
-assert.sameValue(result.length, 3, 'result.length');
-assert.sameValue(result[0], 82, 'result[0]');
-assert.sameValue(result[1], 84, 'result[1]');
-assert.sameValue(result[2], 86, 'result[2]');
+assert.sameValue(result.length, 3, 'The value of result.length is expected to be 3');
+assert.sameValue(result[0], 82, 'The value of result[0] is expected to be 82');
+assert.sameValue(result[1], 84, 'The value of result[1] is expected to be 84');
+assert.sameValue(result[2], 86, 'The value of result[2] is expected to be 86');
 
-assert.sameValue(calls.length, 3, 'calls.length');
+assert.sameValue(calls.length, 3, 'The value of calls.length is expected to be 3');
 
-assert.sameValue(calls[0].args.length, 2, 'calls[0].args.length');
-assert.sameValue(calls[0].args[0], 41, 'calls[0].args[0]');
-assert.sameValue(calls[0].args[1], 0, 'calls[0].args[1]');
-assert.sameValue(calls[0].thisArg, this, 'calls[0].thisArg');
+assert.sameValue(calls[0].args.length, 2, 'The value of calls[0].args.length is expected to be 2');
+assert.sameValue(calls[0].args[0], 41, 'The value of calls[0].args[0] is expected to be 41');
+assert.sameValue(calls[0].args[1], 0, 'The value of calls[0].args[1] is expected to be 0');
+assert.sameValue(calls[0].thisArg, this, 'The value of calls[0].thisArg is expected to be this');
 
-assert.sameValue(calls[1].args.length, 2, 'calls[1].args.length');
-assert.sameValue(calls[1].args[0], 42, 'calls[1].args[0]');
-assert.sameValue(calls[1].args[1], 1, 'calls[1].args[1]');
-assert.sameValue(calls[1].thisArg, this, 'calls[1].thisArg');
+assert.sameValue(calls[1].args.length, 2, 'The value of calls[1].args.length is expected to be 2');
+assert.sameValue(calls[1].args[0], 42, 'The value of calls[1].args[0] is expected to be 42');
+assert.sameValue(calls[1].args[1], 1, 'The value of calls[1].args[1] is expected to be 1');
+assert.sameValue(calls[1].thisArg, this, 'The value of calls[1].thisArg is expected to be this');
 
-assert.sameValue(calls[2].args.length, 2, 'calls[2].args.length');
-assert.sameValue(calls[2].args[0], 43, 'calls[2].args[0]');
-assert.sameValue(calls[2].args[1], 2, 'calls[2].args[1]');
-assert.sameValue(calls[2].thisArg, this, 'calls[2].thisArg');
+assert.sameValue(calls[2].args.length, 2, 'The value of calls[2].args.length is expected to be 2');
+assert.sameValue(calls[2].args[0], 43, 'The value of calls[2].args[0] is expected to be 43');
+assert.sameValue(calls[2].args[1], 2, 'The value of calls[2].args[1] is expected to be 2');
+assert.sameValue(calls[2].thisArg, this, 'The value of calls[2].thisArg is expected to be this');
diff --git a/test/built-ins/Array/from/calling-from-valid-1-onlyStrict.js b/test/built-ins/Array/from/calling-from-valid-1-onlyStrict.js
index 68141450db..d7763285a9 100644
--- a/test/built-ins/Array/from/calling-from-valid-1-onlyStrict.js
+++ b/test/built-ins/Array/from/calling-from-valid-1-onlyStrict.js
@@ -43,24 +43,24 @@ function mapFn(value) {
 
 var result = Array.from(list, mapFn);
 
-assert.sameValue(result.length, 3, 'result.length');
-assert.sameValue(result[0], 82, 'result[0]');
-assert.sameValue(result[1], 84, 'result[1]');
-assert.sameValue(result[2], 86, 'result[2]');
+assert.sameValue(result.length, 3, 'The value of result.length is expected to be 3');
+assert.sameValue(result[0], 82, 'The value of result[0] is expected to be 82');
+assert.sameValue(result[1], 84, 'The value of result[1] is expected to be 84');
+assert.sameValue(result[2], 86, 'The value of result[2] is expected to be 86');
 
-assert.sameValue(calls.length, 3, 'calls.length');
+assert.sameValue(calls.length, 3, 'The value of calls.length is expected to be 3');
 
-assert.sameValue(calls[0].args.length, 2, 'calls[0].args.length');
-assert.sameValue(calls[0].args[0], 41, 'calls[0].args[0]');
-assert.sameValue(calls[0].args[1], 0, 'calls[0].args[1]');
-assert.sameValue(calls[0].thisArg, undefined, 'calls[0].thisArg');
+assert.sameValue(calls[0].args.length, 2, 'The value of calls[0].args.length is expected to be 2');
+assert.sameValue(calls[0].args[0], 41, 'The value of calls[0].args[0] is expected to be 41');
+assert.sameValue(calls[0].args[1], 0, 'The value of calls[0].args[1] is expected to be 0');
+assert.sameValue(calls[0].thisArg, undefined, 'The value of calls[0].thisArg is expected to equal undefined');
 
-assert.sameValue(calls[1].args.length, 2, 'calls[1].args.length');
-assert.sameValue(calls[1].args[0], 42, 'calls[1].args[0]');
-assert.sameValue(calls[1].args[1], 1, 'calls[1].args[1]');
-assert.sameValue(calls[1].thisArg, undefined, 'calls[1].thisArg');
+assert.sameValue(calls[1].args.length, 2, 'The value of calls[1].args.length is expected to be 2');
+assert.sameValue(calls[1].args[0], 42, 'The value of calls[1].args[0] is expected to be 42');
+assert.sameValue(calls[1].args[1], 1, 'The value of calls[1].args[1] is expected to be 1');
+assert.sameValue(calls[1].thisArg, undefined, 'The value of calls[1].thisArg is expected to equal undefined');
 
-assert.sameValue(calls[2].args.length, 2, 'calls[2].args.length');
-assert.sameValue(calls[2].args[0], 43, 'calls[2].args[0]');
-assert.sameValue(calls[2].args[1], 2, 'calls[2].args[1]');
-assert.sameValue(calls[2].thisArg, undefined, 'calls[2].thisArg');
+assert.sameValue(calls[2].args.length, 2, 'The value of calls[2].args.length is expected to be 2');
+assert.sameValue(calls[2].args[0], 43, 'The value of calls[2].args[0] is expected to be 43');
+assert.sameValue(calls[2].args[1], 2, 'The value of calls[2].args[1] is expected to be 2');
+assert.sameValue(calls[2].thisArg, undefined, 'The value of calls[2].thisArg is expected to equal undefined');
diff --git a/test/built-ins/Array/from/calling-from-valid-2.js b/test/built-ins/Array/from/calling-from-valid-2.js
index 2bdfd0d639..5e0d6026e9 100644
--- a/test/built-ins/Array/from/calling-from-valid-2.js
+++ b/test/built-ins/Array/from/calling-from-valid-2.js
@@ -44,24 +44,24 @@ function mapFn(value) {
 
 var result = Array.from(list, mapFn, thisArg);
 
-assert.sameValue(result.length, 3, 'result.length');
-assert.sameValue(result[0], 82, 'result[0]');
-assert.sameValue(result[1], 84, 'result[1]');
-assert.sameValue(result[2], 86, 'result[2]');
+assert.sameValue(result.length, 3, 'The value of result.length is expected to be 3');
+assert.sameValue(result[0], 82, 'The value of result[0] is expected to be 82');
+assert.sameValue(result[1], 84, 'The value of result[1] is expected to be 84');
+assert.sameValue(result[2], 86, 'The value of result[2] is expected to be 86');
 
-assert.sameValue(calls.length, 3, 'calls.length');
+assert.sameValue(calls.length, 3, 'The value of calls.length is expected to be 3');
 
-assert.sameValue(calls[0].args.length, 2, 'calls[0].args.length');
-assert.sameValue(calls[0].args[0], 41, 'calls[0].args[0]');
-assert.sameValue(calls[0].args[1], 0, 'calls[0].args[1]');
-assert.sameValue(calls[0].thisArg, thisArg, 'calls[0].thisArg');
+assert.sameValue(calls[0].args.length, 2, 'The value of calls[0].args.length is expected to be 2');
+assert.sameValue(calls[0].args[0], 41, 'The value of calls[0].args[0] is expected to be 41');
+assert.sameValue(calls[0].args[1], 0, 'The value of calls[0].args[1] is expected to be 0');
+assert.sameValue(calls[0].thisArg, thisArg, 'The value of calls[0].thisArg is expected to equal the value of thisArg');
 
-assert.sameValue(calls[1].args.length, 2, 'calls[1].args.length');
-assert.sameValue(calls[1].args[0], 42, 'calls[1].args[0]');
-assert.sameValue(calls[1].args[1], 1, 'calls[1].args[1]');
-assert.sameValue(calls[1].thisArg, thisArg, 'calls[1].thisArg');
+assert.sameValue(calls[1].args.length, 2, 'The value of calls[1].args.length is expected to be 2');
+assert.sameValue(calls[1].args[0], 42, 'The value of calls[1].args[0] is expected to be 42');
+assert.sameValue(calls[1].args[1], 1, 'The value of calls[1].args[1] is expected to be 1');
+assert.sameValue(calls[1].thisArg, thisArg, 'The value of calls[1].thisArg is expected to equal the value of thisArg');
 
-assert.sameValue(calls[2].args.length, 2, 'calls[2].args.length');
-assert.sameValue(calls[2].args[0], 43, 'calls[2].args[0]');
-assert.sameValue(calls[2].args[1], 2, 'calls[2].args[1]');
-assert.sameValue(calls[2].thisArg, thisArg, 'calls[2].thisArg');
+assert.sameValue(calls[2].args.length, 2, 'The value of calls[2].args.length is expected to be 2');
+assert.sameValue(calls[2].args[0], 43, 'The value of calls[2].args[0] is expected to be 43');
+assert.sameValue(calls[2].args[1], 2, 'The value of calls[2].args[1] is expected to be 2');
+assert.sameValue(calls[2].thisArg, thisArg, 'The value of calls[2].thisArg is expected to equal the value of thisArg');
diff --git a/test/built-ins/Array/from/elements-added-after.js b/test/built-ins/Array/from/elements-added-after.js
index 52900144f5..f6b53d15fa 100644
--- a/test/built-ins/Array/from/elements-added-after.js
+++ b/test/built-ins/Array/from/elements-added-after.js
@@ -22,8 +22,8 @@ var array = [2, 4, 8, 16, 32, 64, 128];
 
 function mapFn(value, index) {
   arrayIndex++;
-  assert.sameValue(value, obj[arrayIndex], "Value mismatch in mapFn at index " + index + ".");
-  assert.sameValue(index, arrayIndex, "Index mismatch in mapFn.");
+  assert.sameValue(value, obj[arrayIndex], 'The value of value is expected to equal the value of obj[arrayIndex]');
+  assert.sameValue(index, arrayIndex, 'The value of index is expected to equal the value of arrayIndex');
   obj[originalLength + arrayIndex] = 2 * arrayIndex + 1;
 
   return obj[arrayIndex];
@@ -31,8 +31,8 @@ function mapFn(value, index) {
 
 
 var a = Array.from(obj, mapFn);
-assert.sameValue(a.length, array.length, "Length mismatch.");
+assert.sameValue(a.length, array.length, 'The value of a.length is expected to equal the value of array.length');
 
 for (var j = 0; j < a.length; j++) {
-  assert.sameValue(a[j], array[j], "Element mismatch for array at index " + j + ".");
+  assert.sameValue(a[j], array[j], 'The value of a[j] is expected to equal the value of array[j]');
 }
diff --git a/test/built-ins/Array/from/elements-deleted-after.js b/test/built-ins/Array/from/elements-deleted-after.js
index bb040550c2..5ee75cbd60 100644
--- a/test/built-ins/Array/from/elements-deleted-after.js
+++ b/test/built-ins/Array/from/elements-deleted-after.js
@@ -15,8 +15,8 @@ var arrayIndex = -1;
 
 function mapFn(value, index) {
   this.arrayIndex++;
-  assert.sameValue(value, array[this.arrayIndex], "Value mismatch in mapFn at index " + index + ".");
-  assert.sameValue(index, this.arrayIndex, "Index mismatch in mapFn.");
+  assert.sameValue(value, array[this.arrayIndex], 'The value of value is expected to equal the value of array[this.arrayIndex]');
+  assert.sameValue(index, this.arrayIndex, 'The value of index is expected to equal the value of this.arrayIndex');
 
   array.splice(array.length - 1, 1);
   return 127;
@@ -25,8 +25,8 @@ function mapFn(value, index) {
 
 a = Array.from(array, mapFn, this);
 
-assert.sameValue(a.length, originalArray.length / 2, "Length mismatch. Old array : " + (originalArray.length / 2) + ". array : " + a.length + ".");
+assert.sameValue(a.length, originalArray.length / 2, 'The value of a.length is expected to be originalArray.length / 2');
 
 for (var j = 0; j < originalArray.length / 2; j++) {
-  assert.sameValue(a[j], 127, "Element mismatch for mapped array at index " + j + ".");
+  assert.sameValue(a[j], 127, 'The value of a[j] is expected to be 127');
 }
diff --git a/test/built-ins/Array/from/elements-updated-after.js b/test/built-ins/Array/from/elements-updated-after.js
index 96a9260aba..b547a21b0f 100644
--- a/test/built-ins/Array/from/elements-updated-after.js
+++ b/test/built-ins/Array/from/elements-updated-after.js
@@ -14,14 +14,14 @@ function mapFn(value, index) {
   if (index + 1 < array.length) {
     array[index + 1] = 127;
   }
-  assert.sameValue(value, 127, "Value mismatch in mapFn at index " + index + ".");
-  assert.sameValue(index, arrayIndex, "Index mismatch in mapFn.");
+  assert.sameValue(value, 127, 'The value of value is expected to be 127');
+  assert.sameValue(index, arrayIndex, 'The value of index is expected to equal the value of arrayIndex');
 
   return value;
 }
 
 var a = Array.from(array, mapFn);
-assert.sameValue(a.length, array.length, "Length mismatch.");
+assert.sameValue(a.length, array.length, 'The value of a.length is expected to equal the value of array.length');
 for (var j = 0; j < a.length; j++) {
-  assert.sameValue(a[j], 127, "Element mismatch for mapped array.");
+  assert.sameValue(a[j], 127, 'The value of a[j] is expected to be 127');
 }
diff --git a/test/built-ins/Array/from/from-array.js b/test/built-ins/Array/from/from-array.js
index ab77bd9460..51e0b6064c 100644
--- a/test/built-ins/Array/from/from-array.js
+++ b/test/built-ins/Array/from/from-array.js
@@ -9,15 +9,15 @@ esid: sec-array.from
 var array = [0, 'foo', , Infinity];
 var result = Array.from(array);
 
-assert.sameValue(result.length, 4, 'result.length');
-assert.sameValue(result[0], 0, 'result[0]');
-assert.sameValue(result[1], 'foo', 'result[1]');
-assert.sameValue(result[2], undefined, 'result[2]');
-assert.sameValue(result[3], Infinity, 'result[3]');
+assert.sameValue(result.length, 4, 'The value of result.length is expected to be 4');
+assert.sameValue(result[0], 0, 'The value of result[0] is expected to be 0');
+assert.sameValue(result[1], 'foo', 'The value of result[1] is expected to be "foo"');
+assert.sameValue(result[2], undefined, 'The value of result[2] is expected to equal undefined');
+assert.sameValue(result[3], Infinity, 'The value of result[3] is expected to equal Infinity');
 
 assert.notSameValue(
   result, array,
-  'result is not the object from items argument'
+  'The value of result is expected to not equal the value of `array`'
 );
 
-assert(result instanceof Array, 'result instanceof Array');
+assert(result instanceof Array, 'The result of evaluating (result instanceof Array) is expected to be true');
diff --git a/test/built-ins/Array/from/from-string.js b/test/built-ins/Array/from/from-string.js
index c4df63f35b..fcb5068378 100644
--- a/test/built-ins/Array/from/from-string.js
+++ b/test/built-ins/Array/from/from-string.js
@@ -10,8 +10,8 @@ author: Hank Yates (hankyates@gmail.com)
 var arrLikeSource = 'Test';
 var result = Array.from(arrLikeSource);
 
-assert.sameValue(result.length, 4, 'result.length');
-assert.sameValue(result[0], 'T', 'result[0]');
-assert.sameValue(result[1], 'e', 'result[1]');
-assert.sameValue(result[2], 's', 'result[2]');
-assert.sameValue(result[3], 't', 'result[3]');
+assert.sameValue(result.length, 4, 'The value of result.length is expected to be 4');
+assert.sameValue(result[0], 'T', 'The value of result[0] is expected to be "T"');
+assert.sameValue(result[1], 'e', 'The value of result[1] is expected to be "e"');
+assert.sameValue(result[2], 's', 'The value of result[2] is expected to be "s"');
+assert.sameValue(result[3], 't', 'The value of result[3] is expected to be "t"');
diff --git a/test/built-ins/Array/from/get-iter-method-err.js b/test/built-ins/Array/from/get-iter-method-err.js
index ad775b6973..321287e33a 100644
--- a/test/built-ins/Array/from/get-iter-method-err.js
+++ b/test/built-ins/Array/from/get-iter-method-err.js
@@ -19,4 +19,4 @@ Object.defineProperty(items, Symbol.iterator, {
 
 assert.throws(Test262Error, function() {
   Array.from(items);
-});
+}, 'Array.from(items) throws a Test262Error exception');
diff --git a/test/built-ins/Array/from/items-is-arraybuffer.js b/test/built-ins/Array/from/items-is-arraybuffer.js
index d936efe736..60c2c6e008 100644
--- a/test/built-ins/Array/from/items-is-arraybuffer.js
+++ b/test/built-ins/Array/from/items-is-arraybuffer.js
@@ -16,4 +16,4 @@ var arrayBuffer = new ArrayBuffer(7);
 
 var result = Array.from(arrayBuffer);
 
-assert.sameValue(result.length, 0);
+assert.sameValue(result.length, 0, 'The value of result.length is expected to be 0');
diff --git a/test/built-ins/Array/from/items-is-null-throws.js b/test/built-ins/Array/from/items-is-null-throws.js
index ca5fa8b3db..a6ada76d01 100644
--- a/test/built-ins/Array/from/items-is-null-throws.js
+++ b/test/built-ins/Array/from/items-is-null-throws.js
@@ -14,4 +14,4 @@ info: |
 
 assert.throws(TypeError, function() {
   Array.from(null);
-});
+}, 'Array.from(null) throws a TypeError exception');
diff --git a/test/built-ins/Array/from/iter-adv-err.js b/test/built-ins/Array/from/iter-adv-err.js
index 38b6181fcd..34cc1174e2 100644
--- a/test/built-ins/Array/from/iter-adv-err.js
+++ b/test/built-ins/Array/from/iter-adv-err.js
@@ -25,4 +25,4 @@ items[Symbol.iterator] = function() {
 
 assert.throws(Test262Error, function() {
   Array.from(items);
-});
+}, 'Array.from(items) throws a Test262Error exception');
diff --git a/test/built-ins/Array/from/iter-cstm-ctor-err.js b/test/built-ins/Array/from/iter-cstm-ctor-err.js
index ff33ed6246..4f29fb4f46 100644
--- a/test/built-ins/Array/from/iter-cstm-ctor-err.js
+++ b/test/built-ins/Array/from/iter-cstm-ctor-err.js
@@ -23,4 +23,4 @@ items[Symbol.iterator] = function() {};
 
 assert.throws(Test262Error, function() {
   Array.from.call(C, items);
-});
+}, 'Array.from.call(C, items) throws a Test262Error exception');
diff --git a/test/built-ins/Array/from/iter-cstm-ctor.js b/test/built-ins/Array/from/iter-cstm-ctor.js
index e73e60a02c..f5eebd8d23 100644
--- a/test/built-ins/Array/from/iter-cstm-ctor.js
+++ b/test/built-ins/Array/from/iter-cstm-ctor.js
@@ -36,13 +36,13 @@ items[Symbol.iterator] = function() {
 result = Array.from.call(C, items);
 
 assert(
-  result instanceof C, 'Constructed value is an instance of the constructor'
+  result instanceof C, 'The result of evaluating (result instanceof C) is expected to be true'
 );
 assert.sameValue(
   result.constructor,
   C,
-  'Constructed value correctly defines a `constructor` property'
+  'The value of result.constructor is expected to equal the value of C'
 );
-assert.sameValue(callCount, 1, 'Constructor invoked exactly once');
-assert.sameValue(thisVal, result, 'Constructed value is returned');
-assert.sameValue(args.length, 0, 'Constructor invoked without arguments');
+assert.sameValue(callCount, 1, 'The value of callCount is expected to be 1');
+assert.sameValue(thisVal, result, 'The value of thisVal is expected to equal the value of result');
+assert.sameValue(args.length, 0, 'The value of args.length is expected to be 0');
diff --git a/test/built-ins/Array/from/iter-get-iter-err.js b/test/built-ins/Array/from/iter-get-iter-err.js
index 2beb85e6db..77dc209833 100644
--- a/test/built-ins/Array/from/iter-get-iter-err.js
+++ b/test/built-ins/Array/from/iter-get-iter-err.js
@@ -12,11 +12,11 @@ info: |
 features: [Symbol.iterator]
 ---*/
 
-var items = {};
-items[Symbol.iterator] = function() {
+var itemsPoisonedSymbolIterator = {};
+itemsPoisonedSymbolIterator[Symbol.iterator] = function() {
   throw new Test262Error();
 };
 
 assert.throws(Test262Error, function() {
-  Array.from(items);
-});
+  Array.from(itemsPoisonedSymbolIterator);
+}, 'Array.from(itemsPoisonedSymbolIterator) throws a Test262Error exception');
diff --git a/test/built-ins/Array/from/iter-get-iter-val-err.js b/test/built-ins/Array/from/iter-get-iter-val-err.js
index 896c671dfd..8f1c1f5143 100644
--- a/test/built-ins/Array/from/iter-get-iter-val-err.js
+++ b/test/built-ins/Array/from/iter-get-iter-val-err.js
@@ -14,14 +14,14 @@ info: |
 features: [Symbol.iterator]
 ---*/
 
-var items = {};
+var itemsPoisonedIteratorValue = {};
 var poisonedValue = {};
 Object.defineProperty(poisonedValue, 'value', {
   get: function() {
     throw new Test262Error();
   }
 });
-items[Symbol.iterator] = function() {
+itemsPoisonedIteratorValue[Symbol.iterator] = function() {
   return {
     next: function() {
       return poisonedValue;
@@ -30,5 +30,5 @@ items[Symbol.iterator] = function() {
 };
 
 assert.throws(Test262Error, function() {
-  Array.from(items);
-});
+  Array.from(itemsPoisonedIteratorValue);
+}, 'Array.from(itemsPoisonedIteratorValue) throws a Test262Error exception');
diff --git a/test/built-ins/Array/from/iter-map-fn-args.js b/test/built-ins/Array/from/iter-map-fn-args.js
index ffba396935..dddb4b790a 100644
--- a/test/built-ins/Array/from/iter-map-fn-args.js
+++ b/test/built-ins/Array/from/iter-map-fn-args.js
@@ -56,16 +56,16 @@ items[Symbol.iterator] = function() {
 
 Array.from(items, mapFn);
 
-assert.sameValue(args.length, 2, 'Iteration count');
+assert.sameValue(args.length, 2, 'The value of args.length is expected to be 2');
 
-assert.sameValue(args[0].length, 2, 'First iteration: arguments length');
+assert.sameValue(args[0].length, 2, 'The value of args[0].length is expected to be 2');
 assert.sameValue(
-  args[0][0], firstResult.value, 'First iteration: first argument'
+  args[0][0], firstResult.value, 'The value of args[0][0] is expected to equal the value of firstResult.value'
 );
-assert.sameValue(args[0][1], 0, 'First iteration: second argument');
+assert.sameValue(args[0][1], 0, 'The value of args[0][1] is expected to be 0');
 
-assert.sameValue(args[1].length, 2, 'Second iteration: arguments length');
+assert.sameValue(args[1].length, 2, 'The value of args[1].length is expected to be 2');
 assert.sameValue(
-  args[1][0], secondResult.value, 'Second iteration: first argument'
+  args[1][0], secondResult.value, 'The value of args[1][0] is expected to equal the value of secondResult.value'
 );
-assert.sameValue(args[1][1], 1, 'Second iteration: second argument');
+assert.sameValue(args[1][1], 1, 'The value of args[1][1] is expected to be 1');
diff --git a/test/built-ins/Array/from/iter-map-fn-err.js b/test/built-ins/Array/from/iter-map-fn-err.js
index 58ba309362..0f589abf01 100644
--- a/test/built-ins/Array/from/iter-map-fn-err.js
+++ b/test/built-ins/Array/from/iter-map-fn-err.js
@@ -36,6 +36,6 @@ items[Symbol.iterator] = function() {
 
 assert.throws(Test262Error, function() {
   Array.from(items, mapFn);
-});
+}, 'Array.from(items, mapFn) throws a Test262Error exception');
 
-assert.sameValue(closeCount, 1);
+assert.sameValue(closeCount, 1, 'The value of closeCount is expected to be 1');
diff --git a/test/built-ins/Array/from/iter-map-fn-return.js b/test/built-ins/Array/from/iter-map-fn-return.js
index 26f70ed51f..70667d487a 100644
--- a/test/built-ins/Array/from/iter-map-fn-return.js
+++ b/test/built-ins/Array/from/iter-map-fn-return.js
@@ -61,6 +61,10 @@ items[Symbol.iterator] = function() {
 
 result = Array.from(items, mapFn);
 
-assert.sameValue(result.length, 2);
-assert.sameValue(result[0], firstReturnVal);
-assert.sameValue(result[1], secondReturnVal);
+assert.sameValue(result.length, 2, 'The value of result.length is expected to be 2');
+assert.sameValue(result[0], firstReturnVal, 'The value of result[0] is expected to equal the value of firstReturnVal');
+assert.sameValue(
+  result[1],
+  secondReturnVal,
+  'The value of result[1] is expected to equal the value of secondReturnVal'
+);
diff --git a/test/built-ins/Array/from/iter-map-fn-this-arg.js b/test/built-ins/Array/from/iter-map-fn-this-arg.js
index 37574af7b6..b72e77fe71 100644
--- a/test/built-ins/Array/from/iter-map-fn-this-arg.js
+++ b/test/built-ins/Array/from/iter-map-fn-this-arg.js
@@ -52,6 +52,6 @@ items[Symbol.iterator] = function() {
 
 Array.from(items, mapFn, thisVal);
 
-assert.sameValue(thisVals.length, 2);
-assert.sameValue(thisVals[0], thisVal, 'First iteration `this` value');
-assert.sameValue(thisVals[1], thisVal, 'Second iteration `this` value');
+assert.sameValue(thisVals.length, 2, 'The value of thisVals.length is expected to be 2');
+assert.sameValue(thisVals[0], thisVal, 'The value of thisVals[0] is expected to equal the value of thisVal');
+assert.sameValue(thisVals[1], thisVal, 'The value of thisVals[1] is expected to equal the value of thisVal');
diff --git a/test/built-ins/Array/from/iter-map-fn-this-non-strict.js b/test/built-ins/Array/from/iter-map-fn-this-non-strict.js
index 47287fb16b..dece8f2f4b 100644
--- a/test/built-ins/Array/from/iter-map-fn-this-non-strict.js
+++ b/test/built-ins/Array/from/iter-map-fn-this-non-strict.js
@@ -55,6 +55,6 @@ items[Symbol.iterator] = function() {
 
 Array.from(items, mapFn);
 
-assert.sameValue(thisVals.length, 2);
-assert.sameValue(thisVals[0], global, 'First iteration `this` value');
-assert.sameValue(thisVals[1], global, 'Second iteration `this` value');
+assert.sameValue(thisVals.length, 2, 'The value of thisVals.length is expected to be 2');
+assert.sameValue(thisVals[0], global, 'The value of thisVals[0] is expected to equal the value of global');
+assert.sameValue(thisVals[1], global, 'The value of thisVals[1] is expected to equal the value of global');
diff --git a/test/built-ins/Array/from/iter-map-fn-this-strict.js b/test/built-ins/Array/from/iter-map-fn-this-strict.js
index 2cf702db44..6ed9ebe4de 100644
--- a/test/built-ins/Array/from/iter-map-fn-this-strict.js
+++ b/test/built-ins/Array/from/iter-map-fn-this-strict.js
@@ -52,6 +52,6 @@ items[Symbol.iterator] = function() {
 
 Array.from(items, mapFn);
 
-assert.sameValue(thisVals.length, 2);
-assert.sameValue(thisVals[0], undefined, 'First iteration `this` value');
-assert.sameValue(thisVals[1], undefined, 'Second iteration `this` value');
+assert.sameValue(thisVals.length, 2, 'The value of thisVals.length is expected to be 2');
+assert.sameValue(thisVals[0], undefined, 'The value of thisVals[0] is expected to equal undefined');
+assert.sameValue(thisVals[1], undefined, 'The value of thisVals[1] is expected to equal undefined');
diff --git a/test/built-ins/Array/from/iter-set-elem-prop-err.js b/test/built-ins/Array/from/iter-set-elem-prop-err.js
index 206074d9e9..f4ca9d6ebf 100644
--- a/test/built-ins/Array/from/iter-set-elem-prop-err.js
+++ b/test/built-ins/Array/from/iter-set-elem-prop-err.js
@@ -16,7 +16,7 @@ info: |
 features: [Symbol.iterator]
 ---*/
 
-var C = function() {
+var constructorSetsIndex0ConfigurableFalse = function() {
   Object.defineProperty(this, '0', {
     writable: true,
     configurable: false
@@ -46,7 +46,7 @@ items[Symbol.iterator] = function() {
 };
 
 assert.throws(TypeError, function() {
-  Array.from.call(C, items);
-});
+  Array.from.call(constructorSetsIndex0ConfigurableFalse, items);
+}, 'Array.from.call(constructorSetsIndex0ConfigurableFalse, items) throws a TypeError exception');
 
-assert.sameValue(closeCount, 1);
+assert.sameValue(closeCount, 1, 'The value of closeCount is expected to be 1');
diff --git a/test/built-ins/Array/from/iter-set-elem-prop.js b/test/built-ins/Array/from/iter-set-elem-prop.js
index abbdf8d227..bf56e64eb9 100644
--- a/test/built-ins/Array/from/iter-set-elem-prop.js
+++ b/test/built-ins/Array/from/iter-set-elem-prop.js
@@ -46,5 +46,13 @@ items[Symbol.iterator] = function() {
 
 result = Array.from(items);
 
-assert.sameValue(result[0], firstIterResult.value);
-assert.sameValue(result[1], secondIterResult.value);
+assert.sameValue(
+  result[0],
+  firstIterResult.value,
+  'The value of result[0] is expected to equal the value of firstIterResult.value'
+);
+assert.sameValue(
+  result[1],
+  secondIterResult.value,
+  'The value of result[1] is expected to equal the value of secondIterResult.value'
+);
diff --git a/test/built-ins/Array/from/iter-set-length-err.js b/test/built-ins/Array/from/iter-set-length-err.js
index 0b459ba03f..4ba52503ce 100644
--- a/test/built-ins/Array/from/iter-set-length-err.js
+++ b/test/built-ins/Array/from/iter-set-length-err.js
@@ -15,9 +15,9 @@ info: |
 features: [Symbol.iterator]
 ---*/
 
-var C = function() {};
+var poisonedPrototypeLength = function() {};
 var items = {};
-Object.defineProperty(C.prototype, 'length', {
+Object.defineProperty(poisonedPrototypeLength.prototype, 'length', {
   set: function(_) {
     throw new Test262Error();
   }
@@ -33,5 +33,5 @@ items[Symbol.iterator] = function() {
 };
 
 assert.throws(Test262Error, function() {
-  Array.from.call(C, items);
-});
+  Array.from.call(poisonedPrototypeLength, items);
+}, 'Array.from.call(poisonedPrototypeLength, items) throws a Test262Error exception');
diff --git a/test/built-ins/Array/from/iter-set-length.js b/test/built-ins/Array/from/iter-set-length.js
index 05e084b2fd..b4639f4ddb 100644
--- a/test/built-ins/Array/from/iter-set-length.js
+++ b/test/built-ins/Array/from/iter-set-length.js
@@ -33,7 +33,7 @@ nextIterResult = lastIterResult = {
 };
 result = Array.from(items);
 
-assert.sameValue(result.length, 0);
+assert.sameValue(result.length, 0, 'The value of result.length is expected to be 0');
 
 nextIterResult = {
   done: false
@@ -43,4 +43,4 @@ lastIterResult = {
 };
 result = Array.from(items);
 
-assert.sameValue(result.length, 1);
+assert.sameValue(result.length, 1, 'The value of result.length is expected to be 1');
diff --git a/test/built-ins/Array/from/mapfn-is-not-callable-typeerror.js b/test/built-ins/Array/from/mapfn-is-not-callable-typeerror.js
index 2275cb725a..c66363d754 100644
--- a/test/built-ins/Array/from/mapfn-is-not-callable-typeerror.js
+++ b/test/built-ins/Array/from/mapfn-is-not-callable-typeerror.js
@@ -15,20 +15,20 @@ info: |
 
 assert.throws(TypeError, function() {
   Array.from([], null);
-});
+}, 'Array.from([], null) throws a TypeError exception');
 
 assert.throws(TypeError, function() {
   Array.from([], {});
-});
+}, 'Array.from([], {}) throws a TypeError exception');
 
 assert.throws(TypeError, function() {
   Array.from([], 'string');
-});
+}, 'Array.from([], "string") throws a TypeError exception');
 
 assert.throws(TypeError, function() {
   Array.from([], true);
-});
+}, 'Array.from([], true) throws a TypeError exception');
 
 assert.throws(TypeError, function() {
   Array.from([], 42);
-});
+}, 'Array.from([], 42) throws a TypeError exception');
diff --git a/test/built-ins/Array/from/mapfn-is-symbol-throws.js b/test/built-ins/Array/from/mapfn-is-symbol-throws.js
index 58b248aba2..7fd7eb9766 100644
--- a/test/built-ins/Array/from/mapfn-is-symbol-throws.js
+++ b/test/built-ins/Array/from/mapfn-is-symbol-throws.js
@@ -17,4 +17,4 @@ features:
 
 assert.throws(TypeError, function() {
   Array.from([], Symbol('1'));
-});
+}, 'Array.from([], Symbol("1")) throws a TypeError exception');
diff --git a/test/built-ins/Array/from/mapfn-throws-exception.js b/test/built-ins/Array/from/mapfn-throws-exception.js
index a87898bf85..6f2a42c0ce 100644
--- a/test/built-ins/Array/from/mapfn-throws-exception.js
+++ b/test/built-ins/Array/from/mapfn-throws-exception.js
@@ -9,10 +9,10 @@ es6id: 22.1.2.1
 
 var array = [2, 4, 8, 16, 32, 64, 128];
 
-function mapFn(value, index, obj) {
+function mapFnThrows(value, index, obj) {
   throw new Test262Error();
 }
 
 assert.throws(Test262Error, function() {
-  Array.from(array, mapFn);
-});
+  Array.from(array, mapFnThrows);
+}, 'Array.from(array, mapFnThrows) throws a Test262Error exception');
diff --git a/test/built-ins/Array/from/not-a-constructor.js b/test/built-ins/Array/from/not-a-constructor.js
index 87f80f7004..4ed9820f0b 100644
--- a/test/built-ins/Array/from/not-a-constructor.js
+++ b/test/built-ins/Array/from/not-a-constructor.js
@@ -25,5 +25,5 @@ assert.sameValue(isConstructor(Array.from), false, 'isConstructor(Array.from) mu
 
 assert.throws(TypeError, () => {
   new Array.from([]);
-}, '`new Array.from([])` throws TypeError');
+}, 'new Array.from([]) throws a TypeError exception');
 
diff --git a/test/built-ins/Array/from/proto-from-ctor-realm.js b/test/built-ins/Array/from/proto-from-ctor-realm.js
index 4439b49646..5bc068c60e 100644
--- a/test/built-ins/Array/from/proto-from-ctor-realm.js
+++ b/test/built-ins/Array/from/proto-from-ctor-realm.js
@@ -28,4 +28,8 @@ C.prototype = null;
 
 var a = Array.from.call(C, []);
 
-assert.sameValue(Object.getPrototypeOf(a), other.Object.prototype);
+assert.sameValue(
+  Object.getPrototypeOf(a),
+  other.Object.prototype,
+  'Object.getPrototypeOf(Array.from.call(C, [])) returns other.Object.prototype'
+);
diff --git a/test/built-ins/Array/from/source-array-boundary.js b/test/built-ins/Array/from/source-array-boundary.js
index 9dad817293..95c60afe43 100644
--- a/test/built-ins/Array/from/source-array-boundary.js
+++ b/test/built-ins/Array/from/source-array-boundary.js
@@ -12,17 +12,17 @@ var arrayIndex = -1;
 
 function mapFn(value, index) {
   this.arrayIndex++;
-  assert.sameValue(value, array[this.arrayIndex], "Value mismatch in mapFn at index " + index + ".");
-  assert.sameValue(index, this.arrayIndex, "Index mismatch in mapFn.");
+  assert.sameValue(value, array[this.arrayIndex], 'The value of value is expected to equal the value of array[this.arrayIndex]');
+  assert.sameValue(index, this.arrayIndex, 'The value of index is expected to equal the value of this.arrayIndex');
 
   return value;
 }
 
 var a = Array.from(array, mapFn, this);
 
-assert.sameValue(a.length, array.length, "Length mismatch.");
-assert.sameValue(a[0], Number.MAX_VALUE, "Element mismatch for mapped array at index 0.");
-assert.sameValue(a[1], Number.MIN_VALUE, "Element mismatch for mapped array at index 1.");
-assert.sameValue(a[2], Number.NaN, "Element mismatch for mapped array at index 2.");
-assert.sameValue(a[3], Number.NEGATIVE_INFINITY, "Element mismatch for mapped array at index 3.");
-assert.sameValue(a[4], Number.POSITIVE_INFINITY, "Element mismatch for mapped array at index 4.");
+assert.sameValue(a.length, array.length, 'The value of a.length is expected to equal the value of array.length');
+assert.sameValue(a[0], Number.MAX_VALUE, 'The value of a[0] is expected to equal the value of Number.MAX_VALUE');
+assert.sameValue(a[1], Number.MIN_VALUE, 'The value of a[1] is expected to equal the value of Number.MIN_VALUE');
+assert.sameValue(a[2], Number.NaN, 'The value of a[2] is expected to equal the value of Number.NaN');
+assert.sameValue(a[3], Number.NEGATIVE_INFINITY, 'The value of a[3] is expected to equal the value of Number.NEGATIVE_INFINITY');
+assert.sameValue(a[4], Number.POSITIVE_INFINITY, 'The value of a[4] is expected to equal the value of Number.POSITIVE_INFINITY');
diff --git a/test/built-ins/Array/from/source-object-constructor.js b/test/built-ins/Array/from/source-object-constructor.js
index 225be5919c..9c6e3d555e 100644
--- a/test/built-ins/Array/from/source-object-constructor.js
+++ b/test/built-ins/Array/from/source-object-constructor.js
@@ -8,4 +8,8 @@ esid: sec-array.from
 es6id: 22.1.2.1
 ---*/
 
-assert.sameValue(Array.from.call(Object, []).constructor, Object);
+assert.sameValue(
+  Array.from.call(Object, []).constructor,
+  Object,
+  'The value of Array.from.call(Object, []).constructor is expected to equal the value of Object'
+);
diff --git a/test/built-ins/Array/from/source-object-iterator-1.js b/test/built-ins/Array/from/source-object-iterator-1.js
index 6ac364ac54..d667de22ff 100644
--- a/test/built-ins/Array/from/source-object-iterator-1.js
+++ b/test/built-ins/Array/from/source-object-iterator-1.js
@@ -29,4 +29,4 @@ var obj = {
 };
 assert.throws(Test262Error, function() {
   Array.from(obj);
-});
+}, 'Array.from(obj) throws a Test262Error exception');
diff --git a/test/built-ins/Array/from/source-object-iterator-2.js b/test/built-ins/Array/from/source-object-iterator-2.js
index 619405c347..f573654605 100644
--- a/test/built-ins/Array/from/source-object-iterator-2.js
+++ b/test/built-ins/Array/from/source-object-iterator-2.js
@@ -31,7 +31,7 @@ var obj = {
   }
 };
 var a = Array.from.call(Object, obj);
-assert.sameValue(typeof a, typeof {}, "The returned type is expected to be object.");
+assert.sameValue(typeof a, typeof {}, 'The value of `typeof a` is expected to be typeof {}');
 for (var j = 0; j < a.length; j++) {
-  assert.sameValue(a[j], array[j], "Elements mismatch at " + j + ".");
+  assert.sameValue(a[j], array[j], 'The value of a[j] is expected to equal the value of array[j]');
 }
diff --git a/test/built-ins/Array/from/source-object-length-set-elem-prop-err.js b/test/built-ins/Array/from/source-object-length-set-elem-prop-err.js
index 2de74eecfa..28789e003f 100644
--- a/test/built-ins/Array/from/source-object-length-set-elem-prop-err.js
+++ b/test/built-ins/Array/from/source-object-length-set-elem-prop-err.js
@@ -38,7 +38,7 @@ var A1 = function(_length) {
 
 assert.throws(TypeError, function() {
   Array.from.call(A1, items);
-});
+}, 'Array.from.call(A1, items) throws a TypeError exception');
 
 var A2 = function(_length) {
   Object.defineProperty(this, "0", {
@@ -49,4 +49,4 @@ var A2 = function(_length) {
 
 assert.throws(TypeError, function() {
   Array.from.call(A2, items);
-});
+}, 'Array.from.call(A2, items) throws a TypeError exception');
diff --git a/test/built-ins/Array/from/source-object-length.js b/test/built-ins/Array/from/source-object-length.js
index 4127f5ec07..77e373a0af 100644
--- a/test/built-ins/Array/from/source-object-length.js
+++ b/test/built-ins/Array/from/source-object-length.js
@@ -21,5 +21,5 @@ var obj = {
 delete obj[2];
 var a = Array.from(obj);
 for (var j = 0; j < expectedArray.length; j++) {
-  assert.sameValue(a[j], expectedArray[j], "Elements mismatch at " + j + ".");
+  assert.sameValue(a[j], expectedArray[j], 'The value of a[j] is expected to equal the value of expectedArray[j]');
 }
diff --git a/test/built-ins/Array/from/source-object-missing.js b/test/built-ins/Array/from/source-object-missing.js
index 3c55030dac..ec4c935fae 100644
--- a/test/built-ins/Array/from/source-object-missing.js
+++ b/test/built-ins/Array/from/source-object-missing.js
@@ -16,7 +16,7 @@ var obj = {
 };
 
 var a = Array.from.call(Object, obj);
-assert.sameValue(typeof a, "object", "The returned type is expected to be object.");
+assert.sameValue(typeof a, "object", 'The value of `typeof a` is expected to be "object"');
 for (var j = 0; j < a.length; j++) {
-  assert.sameValue(a[j], array[j], "Elements mismatch at " + j + ".");
+  assert.sameValue(a[j], array[j], 'The value of a[j] is expected to equal the value of array[j]');
 }
diff --git a/test/built-ins/Array/from/source-object-without.js b/test/built-ins/Array/from/source-object-without.js
index fbb1877822..f3832147a3 100644
--- a/test/built-ins/Array/from/source-object-without.js
+++ b/test/built-ins/Array/from/source-object-without.js
@@ -15,4 +15,4 @@ var obj = {
 }
 
 var a = Array.from(obj);
-assert.sameValue(a.length, 0, "Expected an array of length 0.");
+assert.sameValue(a.length, 0, 'The value of a.length is expected to be 0');
diff --git a/test/built-ins/Array/from/this-null.js b/test/built-ins/Array/from/this-null.js
index c0fa8be227..0ebfe9af10 100644
--- a/test/built-ins/Array/from/this-null.js
+++ b/test/built-ins/Array/from/this-null.js
@@ -8,5 +8,5 @@ description: Does not throw if this is null
 
 var result = Array.from.call(null, []);
 
-assert(result instanceof Array, 'Does not throw if this is null');
-assert.sameValue(result.length, 0, 'result.length');
+assert(result instanceof Array, 'The result of evaluating (result instanceof Array) is expected to be true');
+assert.sameValue(result.length, 0, 'The value of result.length is expected to be 0');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-0-1.js b/test/built-ins/Array/isArray/15.4.3.2-0-1.js
index 15d6b000b2..d5f540fa42 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-0-1.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-0-1.js
@@ -9,4 +9,4 @@ description: Array.isArray must exist as a function
 
 var f = Array.isArray;
 
-assert.sameValue(typeof(f), "function", 'typeof(f)');
+assert.sameValue(typeof f, "function", 'The value of `typeof f` is expected to be "function"');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-0-2.js b/test/built-ins/Array/isArray/15.4.3.2-0-2.js
index 9b18fb0a5e..5b38a2519d 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-0-2.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-0-2.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-0-2
 description: Array.isArray must exist as a function taking 1 parameter
 ---*/
 
-assert.sameValue(Array.isArray.length, 1, 'Array.isArray.length');
+assert.sameValue(Array.isArray.length, 1, 'The value of Array.isArray.length is expected to be 1');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-0-3.js b/test/built-ins/Array/isArray/15.4.3.2-0-3.js
index 299aad0fe8..c9670aeb47 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-0-3.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-0-3.js
@@ -7,7 +7,4 @@ es5id: 15.4.3.2-0-3
 description: Array.isArray return true if its argument is an Array
 ---*/
 
-var a = [];
-var b = Array.isArray(a);
-
-assert.sameValue(b, true, 'b');
+assert.sameValue(Array.isArray([]), true, 'Array.isArray([]) must return true');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-0-4.js b/test/built-ins/Array/isArray/15.4.3.2-0-4.js
index e6b44cd13c..3ec8df1f1e 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-0-4.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-0-4.js
@@ -6,17 +6,9 @@ esid: sec-array.isarray
 description: Array.isArray return false if its argument is not an Array
 ---*/
 
-var b_num = Array.isArray(42);
-var b_undef = Array.isArray(undefined);
-var b_bool = Array.isArray(true);
-var b_str = Array.isArray("abc");
-var b_obj = Array.isArray({});
-var b_null = Array.isArray(null);
-
-
-assert.sameValue(b_num, false, 'b_num');
-assert.sameValue(b_undef, false, 'b_undef');
-assert.sameValue(b_bool, false, 'b_bool');
-assert.sameValue(b_str, false, 'b_str');
-assert.sameValue(b_obj, false, 'b_obj');
-assert.sameValue(b_null, false, 'b_null');
+assert.sameValue(Array.isArray(42), false, 'Array.isArray(42) must return false');
+assert.sameValue(Array.isArray(undefined), false, 'Array.isArray(undefined) must return false');
+assert.sameValue(Array.isArray(true), false, 'Array.isArray(true) must return false');
+assert.sameValue(Array.isArray("abc"), false, 'Array.isArray("abc") must return false');
+assert.sameValue(Array.isArray({}), false, 'Array.isArray({}) must return false');
+assert.sameValue(Array.isArray(null), false, 'Array.isArray(null) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-0-5.js b/test/built-ins/Array/isArray/15.4.3.2-0-5.js
index f6bc9d8235..c8f83b38ea 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-0-5.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-0-5.js
@@ -9,6 +9,4 @@ description: >
     (Array.prototype)
 ---*/
 
-var b = Array.isArray(Array.prototype);
-
-assert.sameValue(b, true, 'b');
+assert.sameValue(Array.isArray(Array.prototype), true, 'Array.isArray(Array.prototype) must return true');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-0-6.js b/test/built-ins/Array/isArray/15.4.3.2-0-6.js
index 1d28be623a..38d6282593 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-0-6.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-0-6.js
@@ -7,7 +7,4 @@ es5id: 15.4.3.2-0-6
 description: Array.isArray return true if its argument is an Array (new Array())
 ---*/
 
-var a = new Array(10);
-var b = Array.isArray(a);
-
-assert.sameValue(b, true, 'b');
+assert.sameValue(Array.isArray(new Array(10)), true, 'Array.isArray(new Array(10)) must return true');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-0-7.js b/test/built-ins/Array/isArray/15.4.3.2-0-7.js
index 87d7f6165f..1d9e6161d4 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-0-7.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-0-7.js
@@ -7,8 +7,4 @@ es5id: 15.4.3.2-0-7
 description: Array.isArray returns false if its argument is not an Array
 ---*/
 
-var o = new Object();
-o[12] = 13;
-var b = Array.isArray(o);
-
-assert.sameValue(b, false, 'b');
+assert.sameValue(Array.isArray({}), false, 'Array.isArray({}) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-1.js b/test/built-ins/Array/isArray/15.4.3.2-1-1.js
index 3c90df63dc..26b8b8e033 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-1.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-1.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-1
 description: Array.isArray applied to boolean primitive
 ---*/
 
-assert.sameValue(Array.isArray(true), false, 'Array.isArray(true)');
+assert.sameValue(Array.isArray(true), false, 'Array.isArray(true) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-10.js b/test/built-ins/Array/isArray/15.4.3.2-1-10.js
index f7f05f3594..cfaa587608 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-10.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-10.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-10
 description: Array.isArray applied to RegExp object
 ---*/
 
-assert.sameValue(Array.isArray(new RegExp()), false, 'Array.isArray(new RegExp())');
+assert.sameValue(Array.isArray(new RegExp()), false, 'Array.isArray(new RegExp()) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-11.js b/test/built-ins/Array/isArray/15.4.3.2-1-11.js
index 98b3d9286d..28c8af6fb7 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-11.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-11.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-11
 description: Array.isArray applied to the JSON object
 ---*/
 
-assert.sameValue(Array.isArray(JSON), false, 'Array.isArray(JSON)');
+assert.sameValue(Array.isArray(JSON), false, 'Array.isArray(JSON) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-12.js b/test/built-ins/Array/isArray/15.4.3.2-1-12.js
index 338db61e79..6d6b0d35a8 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-12.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-12.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-12
 description: Array.isArray applied to Error object
 ---*/
 
-assert.sameValue(Array.isArray(new SyntaxError()), false, 'Array.isArray(new SyntaxError())');
+assert.sameValue(Array.isArray(new SyntaxError()), false, 'Array.isArray(new SyntaxError()) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-13.js b/test/built-ins/Array/isArray/15.4.3.2-1-13.js
index cbc0721a67..6d18149278 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-13.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-13.js
@@ -13,4 +13,4 @@ var arg;
   arg = arguments;
 }(1, 2, 3));
 
-assert.sameValue(Array.isArray(arg), false, 'Array.isArray(arg)');
+assert.sameValue(Array.isArray(arg), false, 'Array.isArray(arguments) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-15.js b/test/built-ins/Array/isArray/15.4.3.2-1-15.js
index 858894f958..c194ea1a09 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-15.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-15.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-15
 description: Array.isArray applied to the global object
 ---*/
 
-assert.sameValue(Array.isArray(this), false, 'Array.isArray(this)');
+assert.sameValue(Array.isArray(this), false, 'Array.isArray(this) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-2.js b/test/built-ins/Array/isArray/15.4.3.2-1-2.js
index 8c621cb621..f3f03deb31 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-2.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-2.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-2
 description: Array.isArray applied to Boolean Object
 ---*/
 
-assert.sameValue(Array.isArray(new Boolean(false)), false, 'Array.isArray(new Boolean(false))');
+assert.sameValue(Array.isArray(new Boolean(false)), false, 'Array.isArray(new Boolean(false)) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-3.js b/test/built-ins/Array/isArray/15.4.3.2-1-3.js
index 615d130ab5..ad5f4ca714 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-3.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-3.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-3
 description: Array.isArray applied to number primitive
 ---*/
 
-assert.sameValue(Array.isArray(5), false, 'Array.isArray(5)');
+assert.sameValue(Array.isArray(5), false, 'Array.isArray(5) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-4.js b/test/built-ins/Array/isArray/15.4.3.2-1-4.js
index 32f925457b..bb4d2dadf5 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-4.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-4.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-4
 description: Array.isArray applied to Number object
 ---*/
 
-assert.sameValue(Array.isArray(new Number(-3)), false, 'Array.isArray(new Number(-3))');
+assert.sameValue(Array.isArray(new Number(-3)), false, 'Array.isArray(new Number(-3)) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-5.js b/test/built-ins/Array/isArray/15.4.3.2-1-5.js
index 3d5f57d8d4..4061a1d7e0 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-5.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-5.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-5
 description: Array.isArray applied to string primitive
 ---*/
 
-assert.sameValue(Array.isArray("abc"), false, 'Array.isArray("abc")');
+assert.sameValue(Array.isArray("abc"), false, 'Array.isArray("abc") must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-6.js b/test/built-ins/Array/isArray/15.4.3.2-1-6.js
index 8c7c190d97..e28df62efc 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-6.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-6.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-6
 description: Array.isArray applied to String object
 ---*/
 
-assert.sameValue(Array.isArray(new String("hello\nworld\\!")), false, 'Array.isArray(new String("hello\nworld\\!"))');
+assert.sameValue(Array.isArray(new String("hello\nworld\\!")), false, 'Array.isArray(new String("hello\\nworld\\\\!")) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-7.js b/test/built-ins/Array/isArray/15.4.3.2-1-7.js
index 412226c330..ec52af4828 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-7.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-7.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-7
 description: Array.isArray applied to Function object
 ---*/
 
-assert.sameValue(Array.isArray(function() {}), false, 'Array.isArray(function () { })');
+assert.sameValue(Array.isArray(function() {}), false, 'Array.isArray(function() {}) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-8.js b/test/built-ins/Array/isArray/15.4.3.2-1-8.js
index c95344a415..6dabc2b19f 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-8.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-8.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-8
 description: Array.isArray applied to the Math object
 ---*/
 
-assert.sameValue(Array.isArray(Math), false, 'Array.isArray(Math)');
+assert.sameValue(Array.isArray(Math), false, 'Array.isArray(Math) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-1-9.js b/test/built-ins/Array/isArray/15.4.3.2-1-9.js
index 177435f060..5d4eab1d01 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-1-9.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-1-9.js
@@ -7,4 +7,4 @@ es5id: 15.4.3.2-1-9
 description: Array.isArray applied to Date object
 ---*/
 
-assert.sameValue(Array.isArray(new Date()), false, 'Array.isArray(new Date())');
+assert.sameValue(Array.isArray(new Date()), false, 'Array.isArray(new Date()) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-2-1.js b/test/built-ins/Array/isArray/15.4.3.2-2-1.js
index d0a5ed7fca..c0311c5bd9 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-2-1.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-2-1.js
@@ -13,4 +13,4 @@ Con.prototype = proto;
 
 var child = new Con();
 
-assert.sameValue(Array.isArray(child), false, 'Array.isArray(child)');
+assert.sameValue(Array.isArray(child), false, 'Array.isArray(new Con()) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-2-2.js b/test/built-ins/Array/isArray/15.4.3.2-2-2.js
index d0bec2d468..3e06236319 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-2-2.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-2-2.js
@@ -15,4 +15,4 @@ Con.prototype = proto;
 
 var child = new Con();
 
-assert.sameValue(Array.isArray(child), false, 'Array.isArray(child)');
+assert.sameValue(Array.isArray(child), false, 'Array.isArray(new Con()) must return false');
diff --git a/test/built-ins/Array/isArray/15.4.3.2-2-3.js b/test/built-ins/Array/isArray/15.4.3.2-2-3.js
index 02da7c1431..f735b29cb8 100644
--- a/test/built-ins/Array/isArray/15.4.3.2-2-3.js
+++ b/test/built-ins/Array/isArray/15.4.3.2-2-3.js
@@ -13,4 +13,4 @@ assert.sameValue(Array.isArray({
   0: 12,
   1: 9,
   length: 2
-}), false, 'Array.isArray({ 0: 12, 1: 9, length: 2 })');
+}), false, 'Array.isArray({0: 12, 1: 9, length: 2}) must return false');
diff --git a/test/built-ins/Array/isArray/name.js b/test/built-ins/Array/isArray/name.js
index 96cdbb0fd4..ed23a4a875 100644
--- a/test/built-ins/Array/isArray/name.js
+++ b/test/built-ins/Array/isArray/name.js
@@ -20,7 +20,7 @@ info: |
 includes: [propertyHelper.js]
 ---*/
 
-assert.sameValue(Array.isArray.name, "isArray");
+assert.sameValue(Array.isArray.name, "isArray", 'The value of Array.isArray.name is expected to be "isArray"');
 
 verifyNotEnumerable(Array.isArray, "name");
 verifyNotWritable(Array.isArray, "name");
diff --git a/test/built-ins/Array/isArray/not-a-constructor.js b/test/built-ins/Array/isArray/not-a-constructor.js
index 4e073d3f7e..a40882453e 100644
--- a/test/built-ins/Array/isArray/not-a-constructor.js
+++ b/test/built-ins/Array/isArray/not-a-constructor.js
@@ -25,5 +25,5 @@ assert.sameValue(isConstructor(Array.isArray), false, 'isConstructor(Array.isArr
 
 assert.throws(TypeError, () => {
   new Array.isArray([]);
-}, '`new Array.isArray([])` throws TypeError');
+}, 'new Array.isArray([]) throws a TypeError exception');
 
diff --git a/test/built-ins/Array/isArray/proxy-revoked.js b/test/built-ins/Array/isArray/proxy-revoked.js
index ba8aa6f2a4..4d21a41524 100644
--- a/test/built-ins/Array/isArray/proxy-revoked.js
+++ b/test/built-ins/Array/isArray/proxy-revoked.js
@@ -25,4 +25,4 @@ handle.revoke();
 
 assert.throws(TypeError, function() {
   Array.isArray(handle.proxy);
-});
+}, 'Array.isArray(handle.proxy) throws a TypeError exception');
diff --git a/test/built-ins/Array/isArray/proxy.js b/test/built-ins/Array/isArray/proxy.js
index 7af7d9ae96..8d6edd72d2 100644
--- a/test/built-ins/Array/isArray/proxy.js
+++ b/test/built-ins/Array/isArray/proxy.js
@@ -23,8 +23,8 @@ var objectProxy = new Proxy({}, {});
 var arrayProxy = new Proxy([], {});
 var arrayProxyProxy = new Proxy(arrayProxy, {});
 
-assert.sameValue(Array.isArray(objectProxy), false);
-assert.sameValue(Array.isArray(arrayProxy), true, 'proxy for array');
+assert.sameValue(Array.isArray(objectProxy), false, 'Array.isArray(new Proxy({}, {})) must return false');
+assert.sameValue(Array.isArray(arrayProxy), true, 'Array.isArray(new Proxy([], {})) must return true');
 assert.sameValue(
-  Array.isArray(arrayProxyProxy), true, 'proxy for proxy for array'
+  Array.isArray(arrayProxyProxy), true, 'Array.isArray(new Proxy(arrayProxy, {})) must return true'
 );
diff --git a/test/built-ins/Array/length.js b/test/built-ins/Array/length.js
index 0d05fccf54..81d052603e 100644
--- a/test/built-ins/Array/length.js
+++ b/test/built-ins/Array/length.js
@@ -17,7 +17,7 @@ info: |
 includes: [propertyHelper.js]
 ---*/
 
-assert.sameValue(Array.length, 1);
+assert.sameValue(Array.length, 1, 'The value of Array.length is expected to be 1');
 
 verifyNotEnumerable(Array, 'length');
 verifyNotWritable(Array, 'length');
diff --git a/test/built-ins/Array/length/15.4.5.1-3.d-1.js b/test/built-ins/Array/length/15.4.5.1-3.d-1.js
index 9525856720..246419f6a8 100644
--- a/test/built-ins/Array/length/15.4.5.1-3.d-1.js
+++ b/test/built-ins/Array/length/15.4.5.1-3.d-1.js
@@ -12,4 +12,4 @@ description: >
 
 assert.throws(RangeError, function() {
   [].length = 4294967296;
-});
+}, '[].length = 4294967296 throws a RangeError exception');
diff --git a/test/built-ins/Array/length/15.4.5.1-3.d-2.js b/test/built-ins/Array/length/15.4.5.1-3.d-2.js
index 2162edb4a2..15c7fd51eb 100644
--- a/test/built-ins/Array/length/15.4.5.1-3.d-2.js
+++ b/test/built-ins/Array/length/15.4.5.1-3.d-2.js
@@ -12,4 +12,4 @@ description: >
 
 assert.throws(RangeError, function() {
   [].length = 4294967297;
-});
+}, '[].length = 4294967297 throws a RangeError exception');
diff --git a/test/built-ins/Array/length/15.4.5.1-3.d-3.js b/test/built-ins/Array/length/15.4.5.1-3.d-3.js
index 7c03867da7..5129809c0d 100644
--- a/test/built-ins/Array/length/15.4.5.1-3.d-3.js
+++ b/test/built-ins/Array/length/15.4.5.1-3.d-3.js
@@ -10,4 +10,4 @@ description: Set array length property to max value 4294967295 (2**32-1,)
 var a = [];
 a.length = 4294967295;
 
-assert.sameValue(a.length, 4294967295, 'a.length');
+assert.sameValue(a.length, 4294967295, 'The value of a.length is expected to be 4294967295');
diff --git a/test/built-ins/Array/length/S15.4.2.2_A1.1_T1.js b/test/built-ins/Array/length/S15.4.2.2_A1.1_T1.js
index 191ee16c1d..dcb71efd62 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A1.1_T1.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A1.1_T1.js
@@ -16,6 +16,4 @@ description: >
 //CHECK#1
 Array.prototype.myproperty = 1;
 var x = new Array(0);
-if (x.myproperty !== 1) {
-  throw new Test262Error('#1: Array.prototype.myproperty = 1; var x = new Array(0); x.myproperty === 1. Actual: ' + (x.myproperty));
-}
+assert.sameValue(x.myproperty, 1, 'The value of x.myproperty is expected to be 1');
diff --git a/test/built-ins/Array/length/S15.4.2.2_A1.1_T2.js b/test/built-ins/Array/length/S15.4.2.2_A1.1_T2.js
index a6743cf2ef..67335367cd 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A1.1_T2.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A1.1_T2.js
@@ -14,6 +14,4 @@ description: Array.prototype.toString = Object.prototype.toString
 //CHECK#1
 Array.prototype.toString = Object.prototype.toString;
 var x = new Array(0);
-if (x.toString() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#1: Array.prototype.toString = Object.prototype.toString; var x = new Array(0); x.toString() === "[object " + "Array" + "]". Actual: ' + (x.toString()));
-}
+assert.sameValue(x.toString(), "[object Array]", 'x.toString() must return "[object Array]"');
diff --git a/test/built-ins/Array/length/S15.4.2.2_A1.1_T3.js b/test/built-ins/Array/length/S15.4.2.2_A1.1_T3.js
index 886e9c801e..3a0d6d34f8 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A1.1_T3.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A1.1_T3.js
@@ -11,7 +11,8 @@ es5id: 15.4.2.2_A1.1_T3
 description: Checking use isPrototypeOf
 ---*/
 
-//CHECK#1
-if (Array.prototype.isPrototypeOf(new Array(0)) !== true) {
-  throw new Test262Error('#1: Array.prototype.isPrototypeOf(new Array(0)) === true. Actual: ' + (Array.prototype.isPrototypeOf(new Array(0))));
-}
+assert.sameValue(
+  Array.prototype.isPrototypeOf(new Array(0)),
+  true,
+  'Array.prototype.isPrototypeOf(new Array(0)) must return true'
+);
diff --git a/test/built-ins/Array/length/S15.4.2.2_A1.2_T1.js b/test/built-ins/Array/length/S15.4.2.2_A1.2_T1.js
index 21c10ee36d..e3e42f096f 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A1.2_T1.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A1.2_T1.js
@@ -10,7 +10,4 @@ description: Checking use Object.prototype.toString
 
 //CHECK#1
 var x = new Array(0);
-x.getClass = Object.prototype.toString;
-if (x.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#1: var x = new Array(0); x.getClass = Object.prototype.toString; x is Array object. Actual: ' + (x.getClass()));
-}
+assert.sameValue(Object.prototype.toString.call(x), "[object Array]", 'Object.prototype.toString.call(new Array(0)) must return "[object Array]"');
diff --git a/test/built-ins/Array/length/S15.4.2.2_A2.1_T1.js b/test/built-ins/Array/length/S15.4.2.2_A2.1_T1.js
index 0e26aa7fc4..bb3d4b5dc6 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A2.1_T1.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A2.1_T1.js
@@ -12,18 +12,12 @@ description: Array constructor is given one argument
 
 //CHECK#1
 var x = new Array(0);
-if (x.length !== 0) {
-  throw new Test262Error('#1: var x = new Array(0); x.length === 0. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 0, 'The value of x.length is expected to be 0');
 
 //CHECK#2
 var x = new Array(1);
-if (x.length !== 1) {
-  throw new Test262Error('#2: var x = new Array(1); x.length === 1. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
 
 //CHECK#3
 var x = new Array(4294967295);
-if (x.length !== 4294967295) {
-  throw new Test262Error('#3: var x = new Array(4294967295); x.length === 4294967295. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 4294967295, 'The value of x.length is expected to be 4294967295');
diff --git a/test/built-ins/Array/length/S15.4.2.2_A2.2_T1.js b/test/built-ins/Array/length/S15.4.2.2_A2.2_T1.js
index 38a1c4c0d9..c2464d6b70 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A2.2_T1.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A2.2_T1.js
@@ -15,9 +15,11 @@ try {
   new Array(-1);
   throw new Test262Error('#1.1: new Array(-1) throw RangeError. Actual: ' + (new Array(-1)));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#1.2: new Array(-1) throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#2
@@ -25,9 +27,11 @@ try {
   new Array(4294967296);
   throw new Test262Error('#2.1: new Array(4294967296) throw RangeError. Actual: ' + (new Array(4294967296)));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#2.2: new Array(4294967296) throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#3
@@ -35,7 +39,9 @@ try {
   new Array(4294967297);
   throw new Test262Error('#3.1: new Array(4294967297) throw RangeError. Actual: ' + (new Array(4294967297)));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#3.2: new Array(4294967297) throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
diff --git a/test/built-ins/Array/length/S15.4.2.2_A2.2_T2.js b/test/built-ins/Array/length/S15.4.2.2_A2.2_T2.js
index e2d0236f61..f60205a1d5 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A2.2_T2.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A2.2_T2.js
@@ -15,9 +15,11 @@ try {
   new Array(NaN);
   throw new Test262Error('#1.1: new Array(NaN) throw RangeError. Actual: ' + (new Array(NaN)));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#1.2: new Array(NaN) throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#2
@@ -25,9 +27,11 @@ try {
   new Array(Number.POSITIVE_INFINITY);
   throw new Test262Error('#2.1: new Array(Number.POSITIVE_INFINITY) throw RangeError. Actual: ' + (new Array(Number.POSITIVE_INFINITY)));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#2.2: new Array(Number.POSITIVE_INFINITY) throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#3
@@ -35,7 +39,9 @@ try {
   new Array(Number.NEGATIVE_INFINITY);
   throw new Test262Error('#3.1: new Array(Number.NEGATIVE_INFINITY) throw RangeError. Actual: ' + (new Array(Number.NEGATIVE_INFINITY)));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#3.2: new Array(Number.NEGATIVE_INFINITY) throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
diff --git a/test/built-ins/Array/length/S15.4.2.2_A2.2_T3.js b/test/built-ins/Array/length/S15.4.2.2_A2.2_T3.js
index 1acd57d360..3422a6e769 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A2.2_T3.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A2.2_T3.js
@@ -15,9 +15,11 @@ try {
   new Array(1.5);
   throw new Test262Error('#1.1: new Array(1.5) throw RangeError. Actual: ' + (new Array(1.5)));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#1.2: new Array(1.5) throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#2
@@ -25,9 +27,11 @@ try {
   new Array(Number.MAX_VALUE);
   throw new Test262Error('#2.1: new Array(Number.MAX_VALUE) throw RangeError. Actual: ' + (new Array(Number.MAX_VALUE)));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#2.2: new Array(Number.MAX_VALUE) throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#3
@@ -35,7 +39,9 @@ try {
   new Array(Number.MIN_VALUE);
   throw new Test262Error('#3.1: new Array(Number.MIN_VALUE) throw RangeError. Actual: ' + (new Array(Number.MIN_VALUE)));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#3.2: new Array(Number.MIN_VALUE) throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
diff --git a/test/built-ins/Array/length/S15.4.2.2_A2.3_T1.js b/test/built-ins/Array/length/S15.4.2.2_A2.3_T1.js
index ef62e29e9c..d8956ca4a6 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A2.3_T1.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A2.3_T1.js
@@ -13,24 +13,10 @@ description: Checking for null and undefined
 
 var x = new Array(null);
 
-//CHECK#1
-if (x.length !== 1) {
-  throw new Test262Error('#1: var x = new Array(null); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#2
-if (x[0] !== null) {
-  throw new Test262Error('#2: var x = new Array(null); x[0] === null. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], null, 'The value of x[0] is expected to be null');
 
 var x = new Array(undefined);
 
-//CHECK#3
-if (x.length !== 1) {
-  throw new Test262Error('#3: var x = new Array(undefined); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#4
-if (x[0] !== undefined) {
-  throw new Test262Error('#4: var x = new Array(undefined); x[0] === undefined. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], undefined, 'The value of x[0] is expected to equal undefined');
diff --git a/test/built-ins/Array/length/S15.4.2.2_A2.3_T2.js b/test/built-ins/Array/length/S15.4.2.2_A2.3_T2.js
index 46159298ca..8654b98203 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A2.3_T2.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A2.3_T2.js
@@ -13,25 +13,11 @@ description: Checking for boolean primitive and Boolean object
 
 var x = new Array(true);
 
-//CHECK#1
-if (x.length !== 1) {
-  throw new Test262Error('#1: var x = new Array(true); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#2
-if (x[0] !== true) {
-  throw new Test262Error('#2: var x = new Array(true); x[0] === true. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], true, 'The value of x[0] is expected to be true');
 
 var obj = new Boolean(false);
 var x = new Array(obj);
 
-//CHECK#3
-if (x.length !== 1) {
-  throw new Test262Error('#3: var obj = new Boolean(false); var x = new Array(obj); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#4
-if (x[0] !== obj) {
-  throw new Test262Error('#4: var obj = new Boolean(false); var x = new Array(obj); x[0] === obj. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], obj, 'The value of x[0] is expected to equal the value of obj');
diff --git a/test/built-ins/Array/length/S15.4.2.2_A2.3_T3.js b/test/built-ins/Array/length/S15.4.2.2_A2.3_T3.js
index 777cab831f..52b15b20d6 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A2.3_T3.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A2.3_T3.js
@@ -13,25 +13,11 @@ description: Checking for boolean primitive and Boolean object
 
 var x = new Array("1");
 
-//CHECK#1
-if (x.length !== 1) {
-  throw new Test262Error('#1: var x = new Array("1"); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#2
-if (x[0] !== "1") {
-  throw new Test262Error('#2: var x = new Array("1"); x[0] === "1". Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], "1", 'The value of x[0] is expected to be "1"');
 
 var obj = new String("0");
 var x = new Array(obj);
 
-//CHECK#3
-if (x.length !== 1) {
-  throw new Test262Error('#3: var obj = new String("0"); var x = new Array(obj); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#4
-if (x[0] !== obj) {
-  throw new Test262Error('#4: var obj = new String("0"); var x = new Array(obj); x[0] === obj. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], obj, 'The value of x[0] is expected to equal the value of obj');
diff --git a/test/built-ins/Array/length/S15.4.2.2_A2.3_T4.js b/test/built-ins/Array/length/S15.4.2.2_A2.3_T4.js
index 1cc04babe7..b9e15435f1 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A2.3_T4.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A2.3_T4.js
@@ -14,38 +14,17 @@ description: Checking for Number object
 var obj = new Number(0);
 var x = new Array(obj);
 
-//CHECK#1
-if (x.length !== 1) {
-  throw new Test262Error('#1: var obj = new Number(0); var x = new Array(obj); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#2
-if (x[0] !== obj) {
-  throw new Test262Error('#2: var obj = new Number(0); var x = new Array(obj); x[0] === obj. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], obj, 'The value of x[0] is expected to equal the value of obj');
 
 var obj = new Number(1);
 var x = new Array(obj);
 
-//CHECK#3
-if (x.length !== 1) {
-  throw new Test262Error('#3: var obj = new Number(1); var x = new Array(obj); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#4
-if (x[0] !== obj) {
-  throw new Test262Error('#4: var obj = new Number(1); var x = new Array(obj); x[0] === obj. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], obj, 'The value of x[0] is expected to equal the value of obj');
 
 var obj = new Number(4294967295);
 var x = new Array(obj);
 
-//CHECK#5
-if (x.length !== 1) {
-  throw new Test262Error('#5: var obj = new Number(4294967295); var x = new Array(obj); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#6
-if (x[0] !== obj) {
-  throw new Test262Error('#6: var obj = new Number(4294967295); var x = new Array(obj); x[0] === obj. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], obj, 'The value of x[0] is expected to equal the value of obj');
diff --git a/test/built-ins/Array/length/S15.4.2.2_A2.3_T5.js b/test/built-ins/Array/length/S15.4.2.2_A2.3_T5.js
index b6e75a3135..b8309614f4 100644
--- a/test/built-ins/Array/length/S15.4.2.2_A2.3_T5.js
+++ b/test/built-ins/Array/length/S15.4.2.2_A2.3_T5.js
@@ -14,38 +14,17 @@ description: Checking for Number object
 var obj = new Number(-1);
 var x = new Array(obj);
 
-//CHECK#1
-if (x.length !== 1) {
-  throw new Test262Error('#1: var obj = new Number(-1); var x = new Array(obj); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#2
-if (x[0] !== obj) {
-  throw new Test262Error('#2: var obj = new Number(-1); var x = new Array(obj); x[0] === obj. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], obj, 'The value of x[0] is expected to equal the value of obj');
 
 var obj = new Number(4294967296);
 var x = new Array(obj);
 
-//CHECK#3
-if (x.length !== 1) {
-  throw new Test262Error('#3: var obj = new Number(4294967296); var x = new Array(obj); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#4
-if (x[0] !== obj) {
-  throw new Test262Error('#4: var obj = new Number(4294967296); var x = new Array(obj); x[0] === obj. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], obj, 'The value of x[0] is expected to equal the value of obj');
 
 var obj = new Number(4294967297);
 var x = new Array(obj);
 
-//CHECK#5
-if (x.length !== 1) {
-  throw new Test262Error('#5: var obj = new Number(4294967297); var x = new Array(obj); x.length === 1. Actual: ' + (x.length));
-}
-
-//CHECK#6
-if (x[0] !== obj) {
-  throw new Test262Error('#6: var obj = new Number(4294967297); var x = new Array(obj); x[0] === obj. Actual: ' + (x[0]));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
+assert.sameValue(x[0], obj, 'The value of x[0] is expected to equal the value of obj');
diff --git a/test/built-ins/Array/length/S15.4.4_A1.3_T1.js b/test/built-ins/Array/length/S15.4.4_A1.3_T1.js
index 0f00555bbd..8c474f7501 100644
--- a/test/built-ins/Array/length/S15.4.4_A1.3_T1.js
+++ b/test/built-ins/Array/length/S15.4.4_A1.3_T1.js
@@ -8,7 +8,4 @@ es5id: 15.4.4_A1.3_T1
 description: Array.prototype.length === 0
 ---*/
 
-//CHECK#1
-if (Array.prototype.length !== 0) {
-  throw new Test262Error('#1.1: Array.prototype.length === 0. Actual: ' + (Array.prototype.length));
-}
+assert.sameValue(Array.prototype.length, 0, 'The value of Array.prototype.length is expected to be 0');
diff --git a/test/built-ins/Array/length/S15.4.5.1_A1.1_T1.js b/test/built-ins/Array/length/S15.4.5.1_A1.1_T1.js
index f39d85ffb4..1e3ae76631 100644
--- a/test/built-ins/Array/length/S15.4.5.1_A1.1_T1.js
+++ b/test/built-ins/Array/length/S15.4.5.1_A1.1_T1.js
@@ -14,9 +14,11 @@ try {
   x.length = 4294967296;
   throw new Test262Error('#1.1: x = []; x.length = 4294967296 throw RangeError. Actual: x.length === ' + (x.length));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#1.2: x = []; x.length = 4294967296 throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#2
@@ -25,9 +27,11 @@ try {
   x.length = -1;
   throw new Test262Error('#2.1: x = []; x.length = -1 throw RangeError. Actual: x.length === ' + (x.length));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#2.2: x = []; x.length = -1 throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#3
@@ -36,7 +40,9 @@ try {
   x.length = 1.5;
   throw new Test262Error('#3.1: x = []; x.length = 1.5 throw RangeError. Actual: x.length === ' + (x.length));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#3.2: x = []; x.length = 1.5 throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
diff --git a/test/built-ins/Array/length/S15.4.5.1_A1.1_T2.js b/test/built-ins/Array/length/S15.4.5.1_A1.1_T2.js
index e5b2f968ba..7d7e71c568 100644
--- a/test/built-ins/Array/length/S15.4.5.1_A1.1_T2.js
+++ b/test/built-ins/Array/length/S15.4.5.1_A1.1_T2.js
@@ -14,9 +14,11 @@ try {
   x.length = NaN;
   throw new Test262Error('#1.1: x = []; x.length = NaN throw RangeError. Actual: x.length === ' + (x.length));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#1.2: x = []; x.length = NaN throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#2
@@ -25,9 +27,11 @@ try {
   x.length = Number.POSITIVE_INFINITY;
   throw new Test262Error('#2.1: x = []; x.length = Number.POSITIVE_INFINITY throw RangeError. Actual: x.length === ' + (x.length));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#2.2: x = []; x.length = Number.POSITIVE_INFINITY throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#3
@@ -36,9 +40,11 @@ try {
   x.length = Number.NEGATIVE_INFINITY;
   throw new Test262Error('#3.1: x = []; x.length = Number.NEGATIVE_INFINITY throw RangeError. Actual: x.length === ' + (x.length));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#3.2: x = []; x.length = Number.NEGATIVE_INFINITY throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
 
 //CHECK#4
@@ -47,7 +53,9 @@ try {
   x.length = undefined;
   throw new Test262Error('#4.1: x = []; x.length = undefined throw RangeError. Actual: x.length === ' + (x.length));
 } catch (e) {
-  if ((e instanceof RangeError) !== true) {
-    throw new Test262Error('#4.2: x = []; x.length = undefined throw RangeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof RangeError,
+    true,
+    'The result of evaluating (e instanceof RangeError) is expected to be true'
+  );
 }
diff --git a/test/built-ins/Array/length/S15.4.5.1_A1.2_T1.js b/test/built-ins/Array/length/S15.4.5.1_A1.2_T1.js
index 3c79e9ae6a..46c7f97378 100644
--- a/test/built-ins/Array/length/S15.4.5.1_A1.2_T1.js
+++ b/test/built-ins/Array/length/S15.4.5.1_A1.2_T1.js
@@ -15,17 +15,9 @@ description: Change length of array
 //CHECK#1
 var x = [0, , 2, , 4];
 x.length = 4;
-if (x[4] !== undefined) {
-  throw new Test262Error('#1: x = [0,,2,,4]; x.length = 4; x[4] === undefined. Actual: ' + (x[4]));
-}
+assert.sameValue(x[4], undefined, 'The value of x[4] is expected to equal undefined');
 
 //CHECK#2
 x.length = 3;
-if (x[3] !== undefined) {
-  throw new Test262Error('#2: x = [0,,2,,4]; x.length = 4; x.length = 3; x[3] === undefined. Actual: ' + (x[3]));
-}
-
-//CHECK#3
-if (x[2] !== 2) {
-  throw new Test262Error('#3: x = [0,,2,,4]; x.length = 4; x.length = 3; x[2] === 2. Actual: ' + (x[2]));
-}
+assert.sameValue(x[3], undefined, 'The value of x[3] is expected to equal undefined');
+assert.sameValue(x[2], 2, 'The value of x[2] is expected to be 2');
diff --git a/test/built-ins/Array/length/S15.4.5.1_A1.2_T3.js b/test/built-ins/Array/length/S15.4.5.1_A1.2_T3.js
index b0cf994de7..e42006bc92 100644
--- a/test/built-ins/Array/length/S15.4.5.1_A1.2_T3.js
+++ b/test/built-ins/Array/length/S15.4.5.1_A1.2_T3.js
@@ -16,12 +16,8 @@ description: Checking an inherited property
 Array.prototype[2] = 2;
 var x = [0, 1];
 x.length = 3;
-if (x.hasOwnProperty('2') !== false) {
-  throw new Test262Error('#1: Array.prototype[2] = 2; x = [0,1]; x.length = 3; x.hasOwnProperty(\'2\') === false. Actual: ' + (x.hasOwnProperty('2')));
-}
+assert.sameValue(x.hasOwnProperty('2'), false, 'x.hasOwnProperty("2") must return false');
 
 //CHECK#2
 x.length = 2;
-if (x[2] !== 2) {
-  throw new Test262Error('#2: Array.prototype[2] = 2; x = [0,1]; x.length = 3; x.length = 2; x[2] === 2. Actual: ' + (x[2]));
-}
+assert.sameValue(x[2], 2, 'The value of x[2] is expected to be 2');
diff --git a/test/built-ins/Array/length/S15.4.5.1_A1.3_T1.js b/test/built-ins/Array/length/S15.4.5.1_A1.3_T1.js
index 06a1201d73..b4dc799fe2 100644
--- a/test/built-ins/Array/length/S15.4.5.1_A1.3_T1.js
+++ b/test/built-ins/Array/length/S15.4.5.1_A1.3_T1.js
@@ -11,41 +11,29 @@ description: length is object or primitve
 //CHECK#1
 var x = [];
 x.length = true;
-if (x.length !== 1) {
-  throw new Test262Error('#1: x = []; x.length = true; x.length === 1. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
 
 //CHECK#2
 x = [0];
 x.length = null;
-if (x.length !== 0) {
-  throw new Test262Error('#2: x = [0]; x.length = null; x.length === 0. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 0, 'The value of x.length is expected to be 0');
 
 //CHECK#3
 x = [0];
 x.length = new Boolean(false);
-if (x.length !== 0) {
-  throw new Test262Error('#3: x = [0]; x.length = new Boolean(false); x.length === 0. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 0, 'The value of x.length is expected to be 0');
 
 //CHECK#4
 x = [];
 x.length = new Number(1);
-if (x.length !== 1) {
-  throw new Test262Error('#4: x = []; x.length = new Number(1); x.length === 1. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
 
 //CHECK#5
 x = [];
 x.length = "1";
-if (x.length !== 1) {
-  throw new Test262Error('#5: x = []; x.length = "1"; x.length === 1. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
 
 //CHECK#6
 x = [];
 x.length = new String("1");
-if (x.length !== 1) {
-  throw new Test262Error('#6: x = []; x.length = new String("1"); x.length === 1. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
diff --git a/test/built-ins/Array/length/S15.4.5.1_A1.3_T2.js b/test/built-ins/Array/length/S15.4.5.1_A1.3_T2.js
index 93d5c95e26..26261f2a19 100644
--- a/test/built-ins/Array/length/S15.4.5.1_A1.3_T2.js
+++ b/test/built-ins/Array/length/S15.4.5.1_A1.3_T2.js
@@ -15,9 +15,7 @@ x.length = {
     return 2
   }
 };
-if (x.length !== 2) {
-  throw new Test262Error('#1: x = []; x.length = {valueOf: function() {return 2}};  x.length === 2. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 2, 'The value of x.length is expected to be 2');
 
 //CHECK#2
 x = [];
@@ -29,9 +27,7 @@ x.length = {
     return 1
   }
 };
-if (x.length !== 2) {
-  throw new Test262Error('#0: x = []; x.length = {valueOf: function() {return 2}, toString: function() {return 1}};  x.length === 2. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 2, 'The value of x.length is expected to be 2');
 
 //CHECK#3
 x = [];
@@ -43,9 +39,7 @@ x.length = {
     return {}
   }
 };
-if (x.length !== 2) {
-  throw new Test262Error('#3: x = []; x.length = {valueOf: function() {return 2}, toString: function() {return {}}};  x.length === 2. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 2, 'The value of x.length is expected to be 2');
 
 //CHECK#4
 try {
@@ -58,16 +52,10 @@ try {
       throw "error"
     }
   };
-  if (x.length !== 2) {
-    throw new Test262Error('#4.1: x = []; x.length = {valueOf: function() {return 2}, toString: function() {throw "error"}}; x.length === ",". Actual: ' + (x.length));
-  }
+  assert.sameValue(x.length, 2, 'The value of x.length is expected to be 2');
 }
 catch (e) {
-  if (e === "error") {
-    throw new Test262Error('#4.2: x = []; x.length = {valueOf: function() {return 2}, toString: function() {throw "error"}}; x.length not throw "error"');
-  } else {
-    throw new Test262Error('#4.3: x = []; x.length = {valueOf: function() {return 2}, toString: function() {throw "error"}}; x.length not throw Error. Actual: ' + (e));
-  }
+  assert.notSameValue(e, "error", 'The value of e is not "error"');
 }
 
 //CHECK#5
@@ -77,9 +65,7 @@ x.length = {
     return 1
   }
 };
-if (x.length !== 1) {
-  throw new Test262Error('#5: x = []; x.length = {toString: function() {return 1}};  x.length === 1. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
 
 //CHECK#6
 x = [];
@@ -91,9 +77,7 @@ x.length = {
     return 1
   }
 }
-if (x.length !== 1) {
-  throw new Test262Error('#6: x = []; x.length = {valueOf: function() {return {}}, toString: function() {return 1}};  x.length === 1. Actual: ' + (x.length));
-}
+assert.sameValue(x.length, 1, 'The value of x.length is expected to be 1');
 
 //CHECK#7
 try {
@@ -110,9 +94,7 @@ try {
   throw new Test262Error('#7.1: x = []; x.length = {valueOf: function() {throw "error"}, toString: function() {return 1}}; x.length throw "error". Actual: ' + (x.length));
 }
 catch (e) {
-  if (e !== "error") {
-    throw new Test262Error('#7.2: x = []; x.length = {valueOf: function() {throw "error"}, toString: function() {return 1}}; x.length throw "error". Actual: ' + (e));
-  }
+  assert.sameValue(e, "error", 'The value of e is expected to be "error"');
 }
 
 //CHECK#8
@@ -130,7 +112,9 @@ try {
   throw new Test262Error('#8.1: x = []; x.length = {valueOf: function() {return {}}, toString: function() {return {}}}  x.length throw TypeError. Actual: ' + (x.length));
 }
 catch (e) {
-  if ((e instanceof TypeError) !== true) {
-    throw new Test262Error('#8.2: x = []; x.length = {valueOf: function() {return {}}, toString: function() {return {}}}  x.length throw TypeError. Actual: ' + (e));
-  }
+  assert.sameValue(
+    e instanceof TypeError,
+    true,
+    'The result of evaluating (e instanceof TypeError) is expected to be true'
+  );
 }
diff --git a/test/built-ins/Array/length/S15.4.5.2_A3_T4.js b/test/built-ins/Array/length/S15.4.5.2_A3_T4.js
index b4f0411c9c..e9f5b8c40c 100644
--- a/test/built-ins/Array/length/S15.4.5.2_A3_T4.js
+++ b/test/built-ins/Array/length/S15.4.5.2_A3_T4.js
@@ -17,22 +17,7 @@ var x = [0, 1, 2];
 x[4294967294] = 4294967294;
 x.length = 2;
 
-//CHECK#1
-if (x[0] !== 0) {
-  throw new Test262Error('#1: x = [0,1,2]; x[4294967294] = 4294967294; x.length = 2; x[0] === 0. Actual: ' + (x[0]));
-}
-
-//CHECK#2
-if (x[1] !== 1) {
-  throw new Test262Error('#2: x = [0,1,2]; x[4294967294] = 4294967294; x.length = 2; x[1] === 1. Actual: ' + (x[1]));
-}
-
-//CHECK#3
-if (x[2] !== undefined) {
-  throw new Test262Error('#3: x = [0,1,2]; x[4294967294] = 4294967294; x.length = 2; x[2] === undefined. Actual: ' + (x[2]));
-}
-
-//CHECK#4
-if (x[4294967294] !== undefined) {
-  throw new Test262Error('#4: x = [0,1,2]; x[4294967294] = 4294967294; x.length = 2; x[4294967294] === undefined. Actual: ' + (x[4294967294]));
-}
+assert.sameValue(x[0], 0, 'The value of x[0] is expected to be 0');
+assert.sameValue(x[1], 1, 'The value of x[1] is expected to be 1');
+assert.sameValue(x[2], undefined, 'The value of x[2] is expected to equal undefined');
+assert.sameValue(x[4294967294], undefined, 'The value of x[4294967294] is expected to equal undefined');
diff --git a/test/built-ins/Array/length/define-own-prop-length-coercion-order-set.js b/test/built-ins/Array/length/define-own-prop-length-coercion-order-set.js
index 0133117cec..c9c35dcb27 100644
--- a/test/built-ins/Array/length/define-own-prop-length-coercion-order-set.js
+++ b/test/built-ins/Array/length/define-own-prop-length-coercion-order-set.js
@@ -32,12 +32,15 @@ length[Symbol.toPrimitive] = function(hint) {
 assert.throws(TypeError, function() {
   "use strict";
   array.length = length;
-});
-assert.compareArray(hints, ["number", "number"]);
+}, '`"use strict"; array.length = length` throws a TypeError exception');
+assert.compareArray(hints, ["number", "number"], 'The value of hints is expected to be ["number", "number"]');
 
 
 array = [1, 2, 3];
 hints = [];
 
-assert(!Reflect.set(array, "length", length));
-assert.compareArray(hints, ["number", "number"]);
+assert(
+  !Reflect.set(array, "length", length),
+  'The value of !Reflect.set(array, "length", length) is expected to be true'
+);
+assert.compareArray(hints, ["number", "number"], 'The value of hints is expected to be ["number", "number"]');
diff --git a/test/built-ins/Array/length/define-own-prop-length-coercion-order.js b/test/built-ins/Array/length/define-own-prop-length-coercion-order.js
index dccb456a26..5b471be372 100644
--- a/test/built-ins/Array/length/define-own-prop-length-coercion-order.js
+++ b/test/built-ins/Array/length/define-own-prop-length-coercion-order.js
@@ -47,12 +47,15 @@ var length = {
 
 assert.throws(TypeError, function() {
   Object.defineProperty(array, "length", {value: length, writable: true});
-});
-assert.sameValue(valueOfCalls, 2);
+}, 'Object.defineProperty(array, "length", {value: length, writable: true}) throws a TypeError exception');
+assert.sameValue(valueOfCalls, 2, 'The value of valueOfCalls is expected to be 2');
 
 
 array = [1, 2];
 valueOfCalls = 0;
 
-assert(!Reflect.defineProperty(array, "length", {value: length, writable: true}));
-assert.sameValue(valueOfCalls, 2);
+assert(
+  !Reflect.defineProperty(array, "length", {value: length, writable: true}),
+  'The value of !Reflect.defineProperty(array, "length", {value: length, writable: true}) is expected to be true'
+);
+assert.sameValue(valueOfCalls, 2, 'The value of valueOfCalls is expected to be 2');
diff --git a/test/built-ins/Array/length/define-own-prop-length-no-value-order.js b/test/built-ins/Array/length/define-own-prop-length-no-value-order.js
index b0f4835761..07538ecc29 100644
--- a/test/built-ins/Array/length/define-own-prop-length-no-value-order.js
+++ b/test/built-ins/Array/length/define-own-prop-length-no-value-order.js
@@ -35,9 +35,12 @@ features: [Reflect]
 
 assert.throws(TypeError, function() {
   Object.defineProperty([], "length", {configurable: true});
-});
+}, 'Object.defineProperty([], "length", {configurable: true}) throws a TypeError exception');
 
-assert(!Reflect.defineProperty([], "length", {enumerable: true}));
+assert(
+  !Reflect.defineProperty([], "length", {enumerable: true}),
+  'The value of !Reflect.defineProperty([], "length", {enumerable: true}) is expected to be true'
+);
 
 assert.throws(TypeError, function() {
   Object.defineProperty([], "length", {
@@ -45,12 +48,15 @@ assert.throws(TypeError, function() {
       throw new Test262Error("[[Get]] shouldn't be called");
     },
   });
-});
+}, 'Object.defineProperty([], "length", {get: function() {throw new Test262Error("[[Get]] shouldn"t be called");},}) throws a TypeError exception');
 
-assert(!Reflect.defineProperty([], "length", {set: function(_value) {}}));
+assert(
+  !Reflect.defineProperty([], "length", {set: function(_value) {}}),
+  'The value of !Reflect.defineProperty([], "length", {set: function(_value) {}}) is expected to be true'
+);
 
 var array = [];
 Object.defineProperty(array, "length", {writable: false});
 assert.throws(TypeError, function() {
   Object.defineProperty(array, "length", {writable: true});
-});
+}, 'Object.defineProperty(array, "length", {writable: true}) throws a TypeError exception');
diff --git a/test/built-ins/Array/length/define-own-prop-length-overflow-order.js b/test/built-ins/Array/length/define-own-prop-length-overflow-order.js
index 1bd7df12a9..a9ba82069f 100644
--- a/test/built-ins/Array/length/define-own-prop-length-overflow-order.js
+++ b/test/built-ins/Array/length/define-own-prop-length-overflow-order.js
@@ -16,14 +16,14 @@ info: |
 
 assert.throws(RangeError, function() {
   Object.defineProperty([], "length", {value: -1, configurable: true});
-});
+}, 'Object.defineProperty([], "length", {value: -1, configurable: true}) throws a RangeError exception');
 
 assert.throws(RangeError, function() {
   Object.defineProperty([], "length", {value: NaN, enumerable: true});
-});
+}, 'Object.defineProperty([], "length", {value: NaN, enumerable: true}) throws a RangeError exception');
 
 var array = [];
 Object.defineProperty(array, "length", {writable: false});
 assert.throws(RangeError, function() {
   Object.defineProperty(array, "length", {value: Number.MAX_SAFE_INTEGER, writable: true});
-});
+}, 'Object.defineProperty(array, "length", {value: Number.MAX_SAFE_INTEGER, writable: true}) throws a RangeError exception');
diff --git a/test/built-ins/Array/length/define-own-prop-length-overflow-realm.js b/test/built-ins/Array/length/define-own-prop-length-overflow-realm.js
index 8b962629f3..cfa4216ca8 100644
--- a/test/built-ins/Array/length/define-own-prop-length-overflow-realm.js
+++ b/test/built-ins/Array/length/define-own-prop-length-overflow-realm.js
@@ -18,4 +18,4 @@ var array = new OArray();
 
 assert.throws(RangeError, function() {
   array.length = 4294967296;
-});
+}, 'array.length = 4294967296 throws a RangeError exception');
diff --git a/test/built-ins/Array/name.js b/test/built-ins/Array/name.js
index 9960493ff1..1b56828736 100644
--- a/test/built-ins/Array/name.js
+++ b/test/built-ins/Array/name.js
@@ -21,7 +21,7 @@ info: |
 includes: [propertyHelper.js]
 ---*/
 
-assert.sameValue(Array.name, 'Array');
+assert.sameValue(Array.name, 'Array', 'The value of Array.name is expected to be "Array"');
 
 verifyNotEnumerable(Array, 'name');
 verifyNotWritable(Array, 'name');
diff --git a/test/built-ins/Array/of/construct-this-with-the-number-of-arguments.js b/test/built-ins/Array/of/construct-this-with-the-number-of-arguments.js
index 1efa2fb4eb..ca13798fb1 100644
--- a/test/built-ins/Array/of/construct-this-with-the-number-of-arguments.js
+++ b/test/built-ins/Array/of/construct-this-with-the-number-of-arguments.js
@@ -24,16 +24,16 @@ function C(length) {
 }
 
 Array.of.call(C);
-assert.sameValue(len, 0, '`Array.of.call(C);` called `new C(0)`');
-assert.sameValue(hits, 1, 'Called constructor once per call');
+assert.sameValue(len, 0, 'The value of len is expected to be 0');
+assert.sameValue(hits, 1, 'The value of hits is expected to be 1');
 
 Array.of.call(C, 'a', 'b')
-assert.sameValue(len, 2, '`Array.of.call(C, "a", "b"));` called `new C(2)`');
-assert.sameValue(hits, 2, 'Called constructor once per call');
+assert.sameValue(len, 2, 'The value of len is expected to be 2');
+assert.sameValue(hits, 2, 'The value of hits is expected to be 2');
 
 Array.of.call(C, false, null, undefined);
 assert.sameValue(
   len, 3,
-  '`Array.of.call(C, false, null, undefined);` called `new C(3)`'
+  'The value of len is expected to be 3'
 );
-assert.sameValue(hits, 3, 'Called constructor once per call');
+assert.sameValue(hits, 3, 'The value of hits is expected to be 3');
diff --git a/test/built-ins/Array/of/creates-a-new-array-from-arguments.js b/test/built-ins/Array/of/creates-a-new-array-from-arguments.js
index fe0d495852..4c4d18b89c 100644
--- a/test/built-ins/Array/of/creates-a-new-array-from-arguments.js
+++ b/test/built-ins/Array/of/creates-a-new-array-from-arguments.js
@@ -25,21 +25,21 @@ info: |
 var a1 = Array.of('Mike', 'Rick', 'Leo');
 assert.sameValue(
   a1.length, 3,
-  'The new array length is the same as the arguments size'
+  'The value of a1.length is expected to be 3'
 );
-assert.sameValue(a1[0], 'Mike', 'set each property in order - #1');
-assert.sameValue(a1[1], 'Rick', 'set each property in order - #2');
-assert.sameValue(a1[2], 'Leo', 'set each property in order - #3');
+assert.sameValue(a1[0], 'Mike', 'The value of a1[0] is expected to be "Mike"');
+assert.sameValue(a1[1], 'Rick', 'The value of a1[1] is expected to be "Rick"');
+assert.sameValue(a1[2], 'Leo', 'The value of a1[2] is expected to be "Leo"');
 
 var a2 = Array.of(undefined, false, null, undefined);
 assert.sameValue(
   a2.length, 4,
-  'Creates an array from the arguments, regarless of their type values'
+  'The value of a2.length is expected to be 4'
 );
-assert.sameValue(a2[0], undefined, 'set each property in order - #1');
-assert.sameValue(a2[1], false, 'set each property in order - #2');
-assert.sameValue(a2[2], null, 'set each property in order - #3');
-assert.sameValue(a2[3], undefined, 'set each property in order - #4');
+assert.sameValue(a2[0], undefined, 'The value of a2[0] is expected to equal undefined');
+assert.sameValue(a2[1], false, 'The value of a2[1] is expected to be false');
+assert.sameValue(a2[2], null, 'The value of a2[2] is expected to be null');
+assert.sameValue(a2[3], undefined, 'The value of a2[3] is expected to equal undefined');
 
 var a3 = Array.of();
-assert.sameValue(a3.length, 0, 'Array.of() returns an empty array');
+assert.sameValue(a3.length, 0, 'The value of a3.length is expected to be 0');
diff --git a/test/built-ins/Array/of/does-not-use-prototype-properties.js b/test/built-ins/Array/of/does-not-use-prototype-properties.js
index 199ecd043a..42c270d4d3 100644
--- a/test/built-ins/Array/of/does-not-use-prototype-properties.js
+++ b/test/built-ins/Array/of/does-not-use-prototype-properties.js
@@ -16,7 +16,7 @@ Object.defineProperty(Array.prototype, "0", {
 });
 
 var arr = Array.of(true);
-assert.sameValue(arr[0], true);
+assert.sameValue(arr[0], true, 'The value of arr[0] is expected to be true');
 
 function Custom() {}
 
@@ -27,4 +27,4 @@ Object.defineProperty(Custom.prototype, "0", {
 });
 
 var custom = Array.of.call(Custom, true);
-assert.sameValue(custom[0], true);
+assert.sameValue(custom[0], true, 'The value of custom[0] is expected to be true');
diff --git a/test/built-ins/Array/of/length.js b/test/built-ins/Array/of/length.js
index 2151f1060a..754d3e6729 100644
--- a/test/built-ins/Array/of/length.js
+++ b/test/built-ins/Array/of/length.js
@@ -13,7 +13,7 @@ includes: [propertyHelper.js]
 
 assert.sameValue(
   Array.of.length, 0,
-  'The value of `Array.of.length` is `0`'
+  'The value of Array.of.length is expected to be 0'
 );
 
 verifyNotEnumerable(Array.of, 'length');
diff --git a/test/built-ins/Array/of/name.js b/test/built-ins/Array/of/name.js
index 5c07646b44..1377a54097 100644
--- a/test/built-ins/Array/of/name.js
+++ b/test/built-ins/Array/of/name.js
@@ -14,7 +14,7 @@ includes: [propertyHelper.js]
 
 assert.sameValue(
   Array.of.name, 'of',
-  'The value of `Array.of.name` is `"of"`'
+  'The value of Array.of.name is expected to be "of"'
 );
 
 verifyNotEnumerable(Array.of, 'name');
diff --git a/test/built-ins/Array/of/not-a-constructor.js b/test/built-ins/Array/of/not-a-constructor.js
index fd725bb541..e79e3a76b0 100644
--- a/test/built-ins/Array/of/not-a-constructor.js
+++ b/test/built-ins/Array/of/not-a-constructor.js
@@ -25,5 +25,5 @@ assert.sameValue(isConstructor(Array.of), false, 'isConstructor(Array.of) must r
 
 assert.throws(TypeError, () => {
   new Array.of(1);
-}, '`new Array.of(1)` throws TypeError');
+}, '`new Array.of(1)` throws a TypeError exception');
 
diff --git a/test/built-ins/Array/of/proto-from-ctor-realm.js b/test/built-ins/Array/of/proto-from-ctor-realm.js
index 6fbe30e9d1..2ede8f4248 100644
--- a/test/built-ins/Array/of/proto-from-ctor-realm.js
+++ b/test/built-ins/Array/of/proto-from-ctor-realm.js
@@ -26,4 +26,8 @@ C.prototype = null;
 
 var a = Array.of.call(C, 1, 2, 3);
 
-assert.sameValue(Object.getPrototypeOf(a), other.Object.prototype);
+assert.sameValue(
+  Object.getPrototypeOf(a),
+  other.Object.prototype,
+  'Object.getPrototypeOf(Array.of.call(C, 1, 2, 3)) returns other.Object.prototype'
+);
diff --git a/test/built-ins/Array/of/return-a-custom-instance.js b/test/built-ins/Array/of/return-a-custom-instance.js
index a144677fca..5f2c8d78ad 100644
--- a/test/built-ins/Array/of/return-a-custom-instance.js
+++ b/test/built-ins/Array/of/return-a-custom-instance.js
@@ -20,18 +20,18 @@ var coop = Array.of.call(Coop, 'Mike', 'Rick', 'Leo');
 
 assert.sameValue(
   coop.length, 3,
-  'Sets a length property with the number of arguments'
+  'The value of coop.length is expected to be 3'
 );
 assert.sameValue(
   coop[0], 'Mike',
-  'Sets each argument in order as integer properties - #1 argument'
+  'The value of coop[0] is expected to be "Mike"'
 );
 assert.sameValue(
   coop[1], 'Rick',
-  'Sets each argument in order as integer properties - #2 argument'
+  'The value of coop[1] is expected to be "Rick"'
 );
 assert.sameValue(
   coop[2], 'Leo',
-  'Sets each argument in order as integer properties - #3 argument'
+  'The value of coop[2] is expected to be "Leo"'
 );
-assert(coop instanceof Coop, 'Returns an instance from a custom constructor');
+assert(coop instanceof Coop, 'The result of evaluating (coop instanceof Coop) is expected to be true');
diff --git a/test/built-ins/Array/of/return-a-new-array-object.js b/test/built-ins/Array/of/return-a-new-array-object.js
index 12e9ba947d..0405dcfc2a 100644
--- a/test/built-ins/Array/of/return-a-new-array-object.js
+++ b/test/built-ins/Array/of/return-a-new-array-object.js
@@ -19,22 +19,22 @@ info: |
 ---*/
 
 var result = Array.of();
-assert(result instanceof Array, 'Array.of() returns a new Array');
+assert(result instanceof Array, 'The result of evaluating (result instanceof Array) is expected to be true');
 
 result = Array.of.call(undefined);
 assert(
   result instanceof Array,
-  'this is not a constructor'
+  'The result of evaluating (result instanceof Array) is expected to be true'
 );
 
 result = Array.of.call(Math.cos);
 assert(
   result instanceof Array,
-  'this is a builtin function with no [[Construct]] slot'
+  'The result of evaluating (result instanceof Array) is expected to be true'
 );
 
 result = Array.of.call(Math.cos.bind(Math));
 assert(
   result instanceof Array,
-  'this is a bound builtin function with no [[Construct]] slot'
+  'The result of evaluating (result instanceof Array) is expected to be true'
 );
diff --git a/test/built-ins/Array/of/return-abrupt-from-contructor.js b/test/built-ins/Array/of/return-abrupt-from-contructor.js
index de955442f5..0b5cd84e5c 100644
--- a/test/built-ins/Array/of/return-abrupt-from-contructor.js
+++ b/test/built-ins/Array/of/return-abrupt-from-contructor.js
@@ -24,4 +24,4 @@ function T() {
 
 assert.throws(Test262Error, function() {
   Array.of.call(T);
-});
+}, 'Array.of.call(T) throws a Test262Error exception');
diff --git a/test/built-ins/Array/of/return-abrupt-from-data-property-using-proxy.js b/test/built-ins/Array/of/return-abrupt-from-data-property-using-proxy.js
index 605741a1a0..774682a8db 100644
--- a/test/built-ins/Array/of/return-abrupt-from-data-property-using-proxy.js
+++ b/test/built-ins/Array/of/return-abrupt-from-data-property-using-proxy.js
@@ -35,4 +35,4 @@ function T() {
 
 assert.throws(Test262Error, function() {
   Array.of.call(T, 'Bob');
-});
+}, 'Array.of.call(T, "Bob") throws a Test262Error exception');
diff --git a/test/built-ins/Array/of/return-abrupt-from-data-property.js b/test/built-ins/Array/of/return-abrupt-from-data-property.js
index 5822ef6fff..29c3bdc7be 100644
--- a/test/built-ins/Array/of/return-abrupt-from-data-property.js
+++ b/test/built-ins/Array/of/return-abrupt-from-data-property.js
@@ -31,7 +31,7 @@ function T1() {
 
 assert.throws(TypeError, function() {
   Array.of.call(T1, 'Bob');
-});
+}, 'Array.of.call(T1, "Bob") throws a TypeError exception');
 
 function T2() {
   Object.defineProperty(this, 0, {
@@ -43,4 +43,4 @@ function T2() {
 
 assert.throws(TypeError, function() {
   Array.of.call(T2, 'Bob');
-})
+}, 'Array.of.call(T2, "Bob") throws a TypeError exception')
diff --git a/test/built-ins/Array/of/return-abrupt-from-setting-length.js b/test/built-ins/Array/of/return-abrupt-from-setting-length.js
index 259bce34e6..282bd90182 100644
--- a/test/built-ins/Array/of/return-abrupt-from-setting-length.js
+++ b/test/built-ins/Array/of/return-abrupt-from-setting-length.js
@@ -23,4 +23,4 @@ function T() {
 
 assert.throws(Test262Error, function() {
   Array.of.call(T);
-});
+}, 'Array.of.call(T) throws a Test262Error exception');
diff --git a/test/built-ins/Array/of/sets-length.js b/test/built-ins/Array/of/sets-length.js
index 765ed93c78..48a7ca52e7 100644
--- a/test/built-ins/Array/of/sets-length.js
+++ b/test/built-ins/Array/of/sets-length.js
@@ -28,9 +28,9 @@ function Pack() {
 
 var result = Array.of.call(Pack, 'wolves', 'cards', 'cigarettes', 'lies');
 
-assert.sameValue(hits, 1, 'instance length setter called once');
+assert.sameValue(hits, 1, 'The value of hits is expected to be 1');
 assert.sameValue(
   value, 4,
-  'setter is called with the number of Array.of arguments'
+  'The value of value is expected to be 4'
 );
-assert.sameValue(_this_, result, 'setter is called with the new object');
+assert.sameValue(_this_, result, 'The value of _this_ is expected to equal the value of result');
diff --git a/test/built-ins/Array/property-cast-boolean-primitive.js b/test/built-ins/Array/property-cast-boolean-primitive.js
index fbe012c720..a721333370 100644
--- a/test/built-ins/Array/property-cast-boolean-primitive.js
+++ b/test/built-ins/Array/property-cast-boolean-primitive.js
@@ -12,9 +12,9 @@ description: Checking for boolean primitive
 var x = [];
 
 x[true] = 1;
-assert.sameValue(x[1], undefined, "x[1]");
-assert.sameValue(x["true"], 1, "x['true']");
+assert.sameValue(x[1], undefined, 'The value of x[1] is expected to equal undefined');
+assert.sameValue(x["true"], 1, 'The value of x["true"] is expected to be 1');
 
 x[false] = 0;
-assert.sameValue(x[0], undefined, "x[0]");
-assert.sameValue(x["false"], 0, "x['false']")
+assert.sameValue(x[0], undefined, 'The value of x[0] is expected to equal undefined');
+assert.sameValue(x["false"], 0, 'The value of x["false"] is expected to be 0')
diff --git a/test/built-ins/Array/property-cast-nan-infinity.js b/test/built-ins/Array/property-cast-nan-infinity.js
index 6c1c57cbe1..f3734f854e 100644
--- a/test/built-ins/Array/property-cast-nan-infinity.js
+++ b/test/built-ins/Array/property-cast-nan-infinity.js
@@ -12,15 +12,15 @@ description: Checking for number primitive
 var x = [];
 
 x[NaN] = 1;
-assert.sameValue(x[0], undefined, "x[NaN] does not cast to x[0]");
-assert.sameValue(x["NaN"], 1, "x[NaN] casts to x['NaN']");
+assert.sameValue(x[0], undefined, 'The value of x[0] is expected to equal undefined');
+assert.sameValue(x["NaN"], 1, 'The value of x["NaN"] is expected to be 1');
 
 var y = [];
 y[Number.POSITIVE_INFINITY] = 1;
-assert.sameValue(y[0], undefined, "y[Number.POSITIVE_INFINITY] !== y[0]");
-assert.sameValue(y["Infinity"], 1, "y[Number.POSITIVE_INFINITY] === y['Infinity']");
+assert.sameValue(y[0], undefined, 'The value of y[0] is expected to equal undefined');
+assert.sameValue(y["Infinity"], 1, 'The value of y["Infinity"] is expected to be 1');
 
 var z = [];
 z[Number.NEGATIVE_INFINITY] = 1;
-assert.sameValue(z[0], undefined, "z[Number.NEGATIVE_INFINITY] !== z[0]");
-assert.sameValue(z["-Infinity"], 1, "z[Number.NEGATIVE_INFINITY] === z['-Infinity']");
+assert.sameValue(z[0], undefined, 'The value of z[0] is expected to equal undefined');
+assert.sameValue(z["-Infinity"], 1, 'The value of z["-Infinity"] is expected to be 1');
diff --git a/test/built-ins/Array/property-cast-number.js b/test/built-ins/Array/property-cast-number.js
index 28cfa7e648..1ba77bd3b3 100644
--- a/test/built-ins/Array/property-cast-number.js
+++ b/test/built-ins/Array/property-cast-number.js
@@ -11,8 +11,8 @@ description: Checking for number primitive
 
 var x = [];
 x[4294967296] = 1;
-assert.sameValue(x[0], undefined, "x[0]");
-assert.sameValue(x["4294967296"], 1, "x['4294967296'] !== 1");
+assert.sameValue(x[0], undefined, 'The value of x[0] is expected to equal undefined');
+assert.sameValue(x["4294967296"], 1, 'The value of x["4294967296"] is expected to be 1');
 
 var y = [];
 y[4294967297] = 1;
diff --git a/test/built-ins/Array/proto-from-ctor-realm-one.js b/test/built-ins/Array/proto-from-ctor-realm-one.js
index 2289a98d4a..650dae54a4 100644
--- a/test/built-ins/Array/proto-from-ctor-realm-one.js
+++ b/test/built-ins/Array/proto-from-ctor-realm-one.js
@@ -31,24 +31,24 @@ var arr;
 
 newTarget.prototype = undefined;
 arr = Reflect.construct(Array, [1], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is undefined');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [1], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = null;
 arr = Reflect.construct(Array, [1], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is null');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [1], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = true;
 arr = Reflect.construct(Array, [1], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a Boolean');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [1], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = '';
 arr = Reflect.construct(Array, [1], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a String');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [1], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = Symbol();
 arr = Reflect.construct(Array, [1], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a Symbol');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [1], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = 0;
 arr = Reflect.construct(Array, [1], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a Number');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [1], newTarget)) returns other.Array.prototype');
diff --git a/test/built-ins/Array/proto-from-ctor-realm-two.js b/test/built-ins/Array/proto-from-ctor-realm-two.js
index 4df83c466e..2b58310e9f 100644
--- a/test/built-ins/Array/proto-from-ctor-realm-two.js
+++ b/test/built-ins/Array/proto-from-ctor-realm-two.js
@@ -31,24 +31,24 @@ var arr;
 
 newTarget.prototype = undefined;
 arr = Reflect.construct(Array, ['a', 'b'], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is undefined');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, ["a", "b"], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = null;
 arr = Reflect.construct(Array, ['a', 'b'], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is null');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, ["a", "b"], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = false;
 arr = Reflect.construct(Array, ['a', 'b'], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a Boolean');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, ["a", "b"], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = '';
 arr = Reflect.construct(Array, ['a', 'b'], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a String');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, ["a", "b"], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = Symbol();
 arr = Reflect.construct(Array, ['a', 'b'], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a Symbol');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, ["a", "b"], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = -1;
 arr = Reflect.construct(Array, ['a', 'b'], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a Number');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, ["a", "b"], newTarget)) returns other.Array.prototype');
diff --git a/test/built-ins/Array/proto-from-ctor-realm-zero.js b/test/built-ins/Array/proto-from-ctor-realm-zero.js
index 17419e0847..1673393e86 100644
--- a/test/built-ins/Array/proto-from-ctor-realm-zero.js
+++ b/test/built-ins/Array/proto-from-ctor-realm-zero.js
@@ -29,24 +29,24 @@ var arr;
 
 newTarget.prototype = undefined;
 arr = Reflect.construct(Array, [], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is undefined');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = null;
 arr = Reflect.construct(Array, [], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is null');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = true;
 arr = Reflect.construct(Array, [], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a Boolean');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = 'str';
 arr = Reflect.construct(Array, [], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a String');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = Symbol();
 arr = Reflect.construct(Array, [], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a Symbol');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [], newTarget)) returns other.Array.prototype');
 
 newTarget.prototype = 1;
 arr = Reflect.construct(Array, [], newTarget);
-assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'newTarget.prototype is a Number');
+assert.sameValue(Object.getPrototypeOf(arr), other.Array.prototype, 'Object.getPrototypeOf(Reflect.construct(Array, [], newTarget)) returns other.Array.prototype');
diff --git a/test/built-ins/Array/proto.js b/test/built-ins/Array/proto.js
index 19ffcba3a8..faff2fc4c4 100644
--- a/test/built-ins/Array/proto.js
+++ b/test/built-ins/Array/proto.js
@@ -12,4 +12,8 @@ info: |
   intrinsic object %FunctionPrototype%.
 ---*/
 
-assert.sameValue(Object.getPrototypeOf(Array), Function.prototype);
+assert.sameValue(
+  Object.getPrototypeOf(Array),
+  Function.prototype,
+  'Object.getPrototypeOf(Array) returns Function.prototype'
+);
diff --git a/test/built-ins/Array/prototype/at/index-argument-tointeger.js b/test/built-ins/Array/prototype/at/index-argument-tointeger.js
index f1f16aece0..6fd87d0c1c 100644
--- a/test/built-ins/Array/prototype/at/index-argument-tointeger.js
+++ b/test/built-ins/Array/prototype/at/index-argument-tointeger.js
@@ -11,7 +11,11 @@ info: |
 
 features: [Array.prototype.at]
 ---*/
-assert.sameValue(typeof Array.prototype.at, 'function');
+assert.sameValue(
+  typeof Array.prototype.at,
+  'function',
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
+);
 
 let valueOfCallCount = 0;
 let index = {
@@ -24,4 +28,4 @@ let index = {
 let a = [0,1,2,3];
 
 assert.sameValue(a.at(index), 1, 'a.at({valueOf() {valueOfCallCount++; return 1;}}) must return 1');
-assert.sameValue(valueOfCallCount, 1, 'The value of `valueOfCallCount` is 1');
+assert.sameValue(valueOfCallCount, 1, 'The value of valueOfCallCount is expected to be 1');
diff --git a/test/built-ins/Array/prototype/at/index-non-numeric-argument-tointeger-invalid.js b/test/built-ins/Array/prototype/at/index-non-numeric-argument-tointeger-invalid.js
index bc379291ca..39c1c38667 100644
--- a/test/built-ins/Array/prototype/at/index-non-numeric-argument-tointeger-invalid.js
+++ b/test/built-ins/Array/prototype/at/index-non-numeric-argument-tointeger-invalid.js
@@ -11,10 +11,14 @@ info: |
 
 features: [Array.prototype.at]
 ---*/
-assert.sameValue(typeof Array.prototype.at, 'function');
+assert.sameValue(
+  typeof Array.prototype.at,
+  'function',
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
+);
 
 let a = [0,1,2,3];
 
 assert.throws(TypeError, () => {
   a.at(Symbol());
-}, '`a.at(Symbol())` throws TypeError');
+}, 'a.at(Symbol()) throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/at/index-non-numeric-argument-tointeger.js b/test/built-ins/Array/prototype/at/index-non-numeric-argument-tointeger.js
index 9de0363826..a1dcf509d9 100644
--- a/test/built-ins/Array/prototype/at/index-non-numeric-argument-tointeger.js
+++ b/test/built-ins/Array/prototype/at/index-non-numeric-argument-tointeger.js
@@ -11,7 +11,11 @@ info: |
 
 features: [Array.prototype.at]
 ---*/
-assert.sameValue(typeof Array.prototype.at, 'function');
+assert.sameValue(
+  typeof Array.prototype.at,
+  'function',
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
+);
 
 let a = [0,1,2,3];
 
diff --git a/test/built-ins/Array/prototype/at/length.js b/test/built-ins/Array/prototype/at/length.js
index 52b33f1307..417084d50e 100644
--- a/test/built-ins/Array/prototype/at/length.js
+++ b/test/built-ins/Array/prototype/at/length.js
@@ -12,11 +12,15 @@ info: |
 includes: [propertyHelper.js]
 features: [Array.prototype.at]
 ---*/
-assert.sameValue(typeof Array.prototype.at, 'function');
+assert.sameValue(
+  typeof Array.prototype.at,
+  'function',
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
+);
 
 assert.sameValue(
   Array.prototype.at.length, 1,
-  'The value of Array.prototype.at.length is 1'
+  'The value of Array.prototype.at.length is expected to be 1'
 );
 
 verifyNotEnumerable(Array.prototype.at, 'length');
diff --git a/test/built-ins/Array/prototype/at/name.js b/test/built-ins/Array/prototype/at/name.js
index 2995f60923..73569c7058 100644
--- a/test/built-ins/Array/prototype/at/name.js
+++ b/test/built-ins/Array/prototype/at/name.js
@@ -12,11 +12,15 @@ info: |
 includes: [propertyHelper.js]
 features: [Array.prototype.at]
 ---*/
-assert.sameValue(typeof Array.prototype.at, 'function');
+assert.sameValue(
+  typeof Array.prototype.at,
+  'function',
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
+);
 
 assert.sameValue(
   Array.prototype.at.name, 'at',
-  'The value of Array.prototype.at.name is "at"'
+  'The value of Array.prototype.at.name is expected to be "at"'
 );
 
 verifyProperty(Array.prototype.at, 'name', {
diff --git a/test/built-ins/Array/prototype/at/prop-desc.js b/test/built-ins/Array/prototype/at/prop-desc.js
index 0a8ee5572d..d3aeba976d 100644
--- a/test/built-ins/Array/prototype/at/prop-desc.js
+++ b/test/built-ins/Array/prototype/at/prop-desc.js
@@ -11,12 +11,16 @@ info: |
 includes: [propertyHelper.js]
 features: [Array.prototype.at]
 ---*/
-assert.sameValue(typeof Array.prototype.at, 'function');
+assert.sameValue(
+  typeof Array.prototype.at,
+  'function',
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
+);
 
 assert.sameValue(
   typeof Array.prototype.at,
   'function',
-  'The value of `typeof Array.prototype.at` is "function"'
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
 );
 
 verifyProperty(Array.prototype, 'at', {
diff --git a/test/built-ins/Array/prototype/at/return-abrupt-from-this.js b/test/built-ins/Array/prototype/at/return-abrupt-from-this.js
index 2613e751b8..abaef88437 100644
--- a/test/built-ins/Array/prototype/at/return-abrupt-from-this.js
+++ b/test/built-ins/Array/prototype/at/return-abrupt-from-this.js
@@ -11,12 +11,16 @@ info: |
 
 features: [Array.prototype.at]
 ---*/
-assert.sameValue(typeof Array.prototype.at, 'function');
+assert.sameValue(
+  typeof Array.prototype.at,
+  'function',
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
+);
 
 assert.throws(TypeError, () => {
   Array.prototype.at.call(undefined);
-}, '`Array.prototype.at.call(undefined)` throws TypeError');
+}, 'Array.prototype.at.call(undefined) throws a TypeError exception');
 
 assert.throws(TypeError, () => {
   Array.prototype.at.call(null);
-}, '`Array.prototype.at.call(null)` throws TypeError');
+}, 'Array.prototype.at.call(null) throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/at/returns-item-relative-index.js b/test/built-ins/Array/prototype/at/returns-item-relative-index.js
index 0c252548f3..06151ffe66 100644
--- a/test/built-ins/Array/prototype/at/returns-item-relative-index.js
+++ b/test/built-ins/Array/prototype/at/returns-item-relative-index.js
@@ -19,12 +19,16 @@ info: |
 
 features: [Array.prototype.at]
 ---*/
-assert.sameValue(typeof Array.prototype.at, 'function');
+assert.sameValue(
+  typeof Array.prototype.at,
+  'function',
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
+);
 
 let a = [1, 2, 3, 4, ,5];
 
 assert.sameValue(a.at(0), 1, 'a.at(0) must return 1');
 assert.sameValue(a.at(-1), 5, 'a.at(-1) must return 5');
-assert.sameValue(a.at(-2), undefined, 'a.at(-2) must return undefined');
+assert.sameValue(a.at(-2), undefined, 'a.at(-2) returns undefined');
 assert.sameValue(a.at(-3), 4, 'a.at(-3) must return 4');
 assert.sameValue(a.at(-4), 3, 'a.at(-4) must return 3');
diff --git a/test/built-ins/Array/prototype/at/returns-item.js b/test/built-ins/Array/prototype/at/returns-item.js
index f6bf36f7d9..6c5acfb9c2 100644
--- a/test/built-ins/Array/prototype/at/returns-item.js
+++ b/test/built-ins/Array/prototype/at/returns-item.js
@@ -19,7 +19,11 @@ info: |
 
 features: [Array.prototype.at]
 ---*/
-assert.sameValue(typeof Array.prototype.at, 'function');
+assert.sameValue(
+  typeof Array.prototype.at,
+  'function',
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
+);
 
 let a = [1, 2, 3, 4,,5];
 
@@ -27,5 +31,5 @@ assert.sameValue(a.at(0), 1, 'a.at(0) must return 1');
 assert.sameValue(a.at(1), 2, 'a.at(1) must return 2');
 assert.sameValue(a.at(2), 3, 'a.at(2) must return 3');
 assert.sameValue(a.at(3), 4, 'a.at(3) must return 4');
-assert.sameValue(a.at(4), undefined, 'a.at(4) must return undefined');
+assert.sameValue(a.at(4), undefined, 'a.at(4) returns undefined');
 assert.sameValue(a.at(5), 5, 'a.at(5) must return 5');
diff --git a/test/built-ins/Array/prototype/at/returns-undefined-for-holes-in-sparse-arrays.js b/test/built-ins/Array/prototype/at/returns-undefined-for-holes-in-sparse-arrays.js
index 83578c1bc1..896d2b573d 100644
--- a/test/built-ins/Array/prototype/at/returns-undefined-for-holes-in-sparse-arrays.js
+++ b/test/built-ins/Array/prototype/at/returns-undefined-for-holes-in-sparse-arrays.js
@@ -22,22 +22,22 @@ features: [Array.prototype.at]
 assert.sameValue(
   typeof Array.prototype.at,
   'function',
-  'The value of `typeof Array.prototype.at` is "function"'
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
 );
 
 let a = [0, 1, , 3, 4, , 6];
 
 assert.sameValue(a.at(0), 0, 'a.at(0) must return 0');
 assert.sameValue(a.at(1), 1, 'a.at(1) must return 1');
-assert.sameValue(a.at(2), undefined, 'a.at(2) must return undefined');
+assert.sameValue(a.at(2), undefined, 'a.at(2) returns undefined');
 assert.sameValue(a.at(3), 3, 'a.at(3) must return 3');
 assert.sameValue(a.at(4), 4, 'a.at(4) must return 4');
-assert.sameValue(a.at(5), undefined, 'a.at(5) must return undefined');
+assert.sameValue(a.at(5), undefined, 'a.at(5) returns undefined');
 assert.sameValue(a.at(6), 6, 'a.at(6) must return 6');
 assert.sameValue(a.at(-0), 0, 'a.at(-0) must return 0');
 assert.sameValue(a.at(-1), 6, 'a.at(-1) must return 6');
-assert.sameValue(a.at(-2), undefined, 'a.at(-2) must return undefined');
+assert.sameValue(a.at(-2), undefined, 'a.at(-2) returns undefined');
 assert.sameValue(a.at(-3), 4, 'a.at(-3) must return 4');
 assert.sameValue(a.at(-4), 3, 'a.at(-4) must return 3');
-assert.sameValue(a.at(-5), undefined, 'a.at(-5) must return undefined');
+assert.sameValue(a.at(-5), undefined, 'a.at(-5) returns undefined');
 assert.sameValue(a.at(-6), 1, 'a.at(-6) must return 1');
diff --git a/test/built-ins/Array/prototype/at/returns-undefined-for-out-of-range-index.js b/test/built-ins/Array/prototype/at/returns-undefined-for-out-of-range-index.js
index f14c045b24..983f82131b 100644
--- a/test/built-ins/Array/prototype/at/returns-undefined-for-out-of-range-index.js
+++ b/test/built-ins/Array/prototype/at/returns-undefined-for-out-of-range-index.js
@@ -10,11 +10,15 @@ info: |
   If k < 0 or k ≥ len, then return undefined.
 features: [Array.prototype.at]
 ---*/
-assert.sameValue(typeof Array.prototype.at, 'function');
+assert.sameValue(
+  typeof Array.prototype.at,
+  'function',
+  'The value of `typeof Array.prototype.at` is expected to be "function"'
+);
 
 let a = [];
 
-assert.sameValue(a.at(-2), undefined, 'a.at(-2) must return undefined'); // wrap around the end
-assert.sameValue(a.at(0), undefined, 'a.at(0) must return undefined');
-assert.sameValue(a.at(1), undefined, 'a.at(1) must return undefined');
+assert.sameValue(a.at(-2), undefined, 'a.at(-2) returns undefined'); // wrap around the end
+assert.sameValue(a.at(0), undefined, 'a.at(0) returns undefined');
+assert.sameValue(a.at(1), undefined, 'a.at(1) returns undefined');
 
diff --git a/test/built-ins/Array/prototype/concat/15.4.4.4-5-c-i-1.js b/test/built-ins/Array/prototype/concat/15.4.4.4-5-c-i-1.js
index 274d5b83b7..319cea0fe2 100644
--- a/test/built-ins/Array/prototype/concat/15.4.4.4-5-c-i-1.js
+++ b/test/built-ins/Array/prototype/concat/15.4.4.4-5-c-i-1.js
@@ -15,10 +15,13 @@ Object.defineProperty(Array.prototype, "0", {
   configurable: true
 });
 
-var newArr = Array.prototype.concat.call(101);
+var newArrayFromConcat = Array.prototype.concat.call(101);
 
-assert(newArr[0] instanceof Number);
-verifyProperty(newArr, "0", {
+assert(
+  newArrayFromConcat[0] instanceof Number,
+  'The result of evaluating (newArrayFromConcat[0] instanceof Number) is expected to be true'
+);
+verifyProperty(newArrayFromConcat, "0", {
   writable: true,
   enumerable: true,
   configurable: true,
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-length-to-string-throws.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-length-to-string-throws.js
index c8e6a5d562..1915720abe 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-length-to-string-throws.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-length-to-string-throws.js
@@ -7,11 +7,10 @@ esid: sec-array.prototype.concat
 description: Array.prototype.concat array like length to string throws
 features: [Symbol.isConcatSpreadable]
 ---*/
-function MyError() {}
-var obj = {
+var objWithPoisonedLengthToString = {
   "length": {
     toString: function() {
-      throw new MyError();
+      throw new Test262Error();
     },
     valueOf: null
   },
@@ -19,7 +18,7 @@ var obj = {
   "3": "B",
   "5": "C"
 };
-obj[Symbol.isConcatSpreadable] = true;
-assert.throws(MyError, function() {
-  [].concat(obj);
-});
+objWithPoisonedLengthToString[Symbol.isConcatSpreadable] = true;
+assert.throws(Test262Error, function() {
+  [].concat(objWithPoisonedLengthToString);
+}, '[].concat(objWithPoisonedLengthToString) throws a Test262Error exception');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-length-value-of-throws.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-length-value-of-throws.js
index 4ff54c415e..6e457ada74 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-length-value-of-throws.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-length-value-of-throws.js
@@ -7,11 +7,10 @@ esid: sec-array.prototype.concat
 description: Array.prototype.concat array like length valueOf throws
 features: [Symbol.isConcatSpreadable]
 ---*/
-function MyError() {}
-var obj = {
+var objWithPoisonedLengthValueOf = {
   "length": {
     valueOf: function() {
-      throw new MyError();
+      throw new Test262Error();
     },
     toString: null
   },
@@ -19,7 +18,7 @@ var obj = {
   "3": "B",
   "5": "C"
 };
-obj[Symbol.isConcatSpreadable] = true;
-assert.throws(MyError, function() {
-  [].concat(obj);
-});
+objWithPoisonedLengthValueOf[Symbol.isConcatSpreadable] = true;
+assert.throws(Test262Error, function() {
+  [].concat(objWithPoisonedLengthValueOf);
+}, '[].concat(objWithPoisonedLengthValueOf) throws a Test262Error exception');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-negative-length.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-negative-length.js
index 1e6cfb8dff..9f4ba09169 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-negative-length.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-negative-length.js
@@ -15,8 +15,8 @@ var obj = {
   "5": "C"
 };
 obj[Symbol.isConcatSpreadable] = true;
-assert(compareArray([].concat(obj), []));
+assert.compareArray([].concat(obj), [], '[].concat({"length": -4294967294, "1": "A", "3": "B", "5": "C"}) must return []');
 obj.length = -4294967294;
-assert(compareArray([].concat(obj), []));
+assert.compareArray([].concat(obj), [], '[].concat({"length": -4294967294, "1": "A", "3": "B", "5": "C"}) must return []');
 obj.length = "-4294967294";
-assert(compareArray([].concat(obj), []));
+assert.compareArray([].concat(obj), [], '[].concat({"length": -4294967294, "1": "A", "3": "B", "5": "C"}) must return []');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-primitive-non-number-length.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-primitive-non-number-length.js
index cc4506710d..27a19e058d 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-primitive-non-number-length.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-primitive-non-number-length.js
@@ -20,11 +20,11 @@ obj.length = {
   },
   valueOf: null
 };
-assert(compareArray([].concat(obj), []));
+assert.compareArray([].concat(obj), [], '[].concat({"1": "A", "3": "B", "5": "C"}) must return []');
 obj.length = {
   toString: null,
   valueOf: function() {
     return "SIX";
   }
 };
-assert(compareArray([].concat(obj), []));
+assert.compareArray([].concat(obj), [], '[].concat({"1": "A", "3": "B", "5": "C"}) must return []');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-string-length.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-string-length.js
index 6323bd8cdb..52401177df 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-string-length.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-string-length.js
@@ -30,4 +30,4 @@ var expected = [
 ];
 var actual = Array.prototype.concat.call(obj, obj2, arr);
 
-assert(compareArray(actual, expected));
+assert.compareArray(actual, expected, 'The value of actual is expected to equal the value of expected');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-to-length-throws.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-to-length-throws.js
index e5a440ca16..64effc7993 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-to-length-throws.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like-to-length-throws.js
@@ -7,7 +7,7 @@ esid: sec-array.prototype.concat
 description: Array.prototype.concat array like to length throws
 features: [Symbol.isConcatSpreadable]
 ---*/
-var obj = {
+var spreadableWithBrokenLength = {
   "length": {
     valueOf: null,
     toString: null
@@ -16,7 +16,7 @@ var obj = {
   "3": "B",
   "5": "C"
 };
-obj[Symbol.isConcatSpreadable] = true;
+spreadableWithBrokenLength[Symbol.isConcatSpreadable] = true;
 var obj2 = {
   length: 3,
   "0": "0",
@@ -25,5 +25,5 @@ var obj2 = {
 };
 var arr = ["X", "Y", "Z"];
 assert.throws(TypeError, function() {
-  Array.prototype.concat.call(obj, obj2, arr);
-});
+  Array.prototype.concat.call(spreadableWithBrokenLength, obj2, arr);
+}, 'Array.prototype.concat.call(spreadableWithBrokenLength, obj2, arr) throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like.js
index 402f31c6cc..e8782cef10 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_array-like.js
@@ -31,4 +31,4 @@ var expected = [
 ];
 var actual = Array.prototype.concat.call(obj, obj2, arr);
 
-assert(compareArray(actual, expected));
+assert.compareArray(actual, expected, 'The value of actual is expected to equal the value of expected');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_holey-sloppy-arguments.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_holey-sloppy-arguments.js
index 8e984e50aa..d4c562028f 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_holey-sloppy-arguments.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_holey-sloppy-arguments.js
@@ -14,4 +14,6 @@ var args = (function(a) {
 })(1, 2, 3);
 delete args[1];
 args[Symbol.isConcatSpreadable] = true;
-assert(compareArray([1, void 0, 3, 1, void 0, 3], [].concat(args, args)));
+assert.compareArray([1, void 0, 3, 1, void 0, 3], [].concat(args, args),
+  '[1, void 0, 3, 1, void 0, 3] must return the same value returned by [].concat(args, args)'
+);
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_large-typed-array.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_large-typed-array.js
index 38419927b1..361a990748 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_large-typed-array.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_large-typed-array.js
@@ -16,13 +16,22 @@ function concatTypedArray(type, elems, modulo) {
     ta_by_len[i] = items[i] = modulo === false ? i : elems % modulo;
   }
   var ta = new type(items);
-  assert(compareArray([].concat(ta, ta), [ta, ta]));
+  assert(
+    compareArray([].concat(ta, ta), [ta, ta]),
+    'compareArray([].concat(ta, ta), [ta, ta]) must return true'
+  );
   ta[Symbol.isConcatSpreadable] = true;
-  assert(compareArray([].concat(ta), items));
+  assert.compareArray([].concat(ta), items, '[].concat(new type(items)) returns items');
 
-  assert(compareArray([].concat(ta_by_len, ta_by_len), [ta_by_len, ta_by_len]));
+  assert(
+    compareArray([].concat(ta_by_len, ta_by_len), [ta_by_len, ta_by_len]),
+    'compareArray([].concat(ta_by_len, ta_by_len), [ta_by_len, ta_by_len]) must return true'
+  );
   ta_by_len[Symbol.isConcatSpreadable] = true;
-  assert(compareArray([].concat(ta_by_len), items));
+  assert(
+    compareArray([].concat(ta_by_len), items),
+    'compareArray([].concat(ta_by_len), items) must return true'
+  );
 
   // TypedArray with fake `length`.
   ta = new type(1);
@@ -34,7 +43,7 @@ function concatTypedArray(type, elems, modulo) {
     value: 4000
   });
   ta[Symbol.isConcatSpreadable] = true;
-  assert(compareArray([].concat(ta), expected));
+  assert.compareArray([].concat(ta), expected, '[].concat(new type(1)) returns expected');
 }
 
 var max = [Math.pow(2, 8), Math.pow(2, 16), Math.pow(2, 32), false, false];
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_length-throws.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_length-throws.js
index eee6036f5a..63b65a2eb8 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_length-throws.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_length-throws.js
@@ -8,19 +8,18 @@ esid: sec-array.prototype.concat
 description: Array.prototype.concat length throws
 features: [Symbol.isConcatSpreadable]
 ---*/
-function MyError() {}
-var obj = {};
-obj[Symbol.isConcatSpreadable] = true;
-Object.defineProperty(obj, "length", {
+var spreadablePoisonedLengthGetter = {};
+spreadablePoisonedLengthGetter[Symbol.isConcatSpreadable] = true;
+Object.defineProperty(spreadablePoisonedLengthGetter, "length", {
   get: function() {
-    throw new MyError();
+    throw new Test262Error();
   }
 });
 
-assert.throws(MyError, function() {
-  [].concat(obj);
-});
+assert.throws(Test262Error, function() {
+  [].concat(spreadablePoisonedLengthGetter);
+}, '[].concat(spreadablePoisonedLengthGetter) throws a Test262Error exception');
 
-assert.throws(MyError, function() {
-  Array.prototype.concat.call(obj, 1, 2, 3);
-});
+assert.throws(Test262Error, function() {
+  Array.prototype.concat.call(spreadablePoisonedLengthGetter, 1, 2, 3);
+}, 'Array.prototype.concat.call(spreadablePoisonedLengthGetter, 1, 2, 3) throws a Test262Error exception');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_no-prototype.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_no-prototype.js
index 81e8ee2698..1cd134348d 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_no-prototype.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_no-prototype.js
@@ -7,4 +7,8 @@
 esid: sec-array.prototype.concat
 description: Array.prototype.concat no prototype
 ---*/
-assert.sameValue(Array.prototype.concat.prototype, void 0);
+assert.sameValue(
+  Array.prototype.concat.prototype,
+  void 0,
+  'The value of Array.prototype.concat.prototype is expected to be void 0'
+);
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_non-array.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_non-array.js
index edb905f1e1..f15bb55afc 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_non-array.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_non-array.js
@@ -20,6 +20,10 @@ class NonArray {
 
 var obj = new NonArray(1, 2, 3);
 var result = Array.prototype.concat.call(obj, 4, 5, 6);
-assert.sameValue(Array, result.constructor);
-assert.sameValue(result instanceof NonArray, false);
-assert(compareArray(result, [obj, 4, 5, 6]));
+assert.sameValue(Array, result.constructor, 'The value of Array is expected to equal the value of result.constructor');
+assert.sameValue(
+  result instanceof NonArray,
+  false,
+  'The result of evaluating (result instanceof NonArray) is expected to be false'
+);
+assert.compareArray(result, [obj, 4, 5, 6], 'The value of result is expected to be [obj, 4, 5, 6]');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments-throws.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments-throws.js
index f72b237e1d..192accf57c 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments-throws.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments-throws.js
@@ -8,16 +8,15 @@ esid: sec-array.prototype.concat
 description: Array.prototype.concat sloppy arguments throws
 features: [Symbol.isConcatSpreadable]
 ---*/
-function MyError() {}
 var args = (function(a) {
   return arguments;
 })(1, 2, 3);
 Object.defineProperty(args, 0, {
   get: function() {
-    throw new MyError();
+    throw new Test262Error();
   }
 });
 args[Symbol.isConcatSpreadable] = true;
-assert.throws(MyError, function() {
+assert.throws(Test262Error, function() {
   return [].concat(args, args);
-});
+}, 'return [].concat(args, args) throws a Test262Error exception');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments-with-dupes.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments-with-dupes.js
index abdaed774f..6943e1b7a9 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments-with-dupes.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments-with-dupes.js
@@ -14,9 +14,13 @@ var args = (function(a, a, a) {
   return arguments;
 })(1, 2, 3);
 args[Symbol.isConcatSpreadable] = true;
-assert(compareArray([].concat(args, args), [1, 2, 3, 1, 2, 3]));
+assert.compareArray([].concat(args, args), [1, 2, 3, 1, 2, 3],
+  '[].concat((function(a, a, a) {return arguments;})(1, 2, 3), (function(a, a, a) {return arguments;})(1, 2, 3)) must return [1, 2, 3, 1, 2, 3]'
+);
 
 Object.defineProperty(args, "length", {
   value: 6
 });
-assert(compareArray([].concat(args), [1, 2, 3, void 0, void 0, void 0]));
+assert.compareArray([].concat(args), [1, 2, 3, void 0, void 0, void 0],
+  '[].concat((function(a, a, a) {return arguments;})(1, 2, 3)) must return [1, 2, 3, void 0, void 0, void 0]'
+);
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments.js
index 50af3bbe33..0303cd9a38 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_sloppy-arguments.js
@@ -13,9 +13,13 @@ var args = (function(a, b, c) {
   return arguments;
 })(1, 2, 3);
 args[Symbol.isConcatSpreadable] = true;
-assert(compareArray([].concat(args, args), [1, 2, 3, 1, 2, 3]));
+assert.compareArray([].concat(args, args), [1, 2, 3, 1, 2, 3],
+  '[].concat((function(a, b, c) {return arguments;})(1, 2, 3), (function(a, b, c) {return arguments;})(1, 2, 3)) must return [1, 2, 3, 1, 2, 3]'
+);
 
 Object.defineProperty(args, "length", {
   value: 6
 });
-assert(compareArray([].concat(args), [1, 2, 3, void 0, void 0, void 0]));
+assert.compareArray([].concat(args), [1, 2, 3, void 0, void 0, void 0],
+  '[].concat((function(a, b, c) {return arguments;})(1, 2, 3)) must return [1, 2, 3, void 0, void 0, void 0]'
+);
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_small-typed-array.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_small-typed-array.js
index 64ded54db5..4c8763a9d9 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_small-typed-array.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_small-typed-array.js
@@ -16,13 +16,22 @@ function concatTypedArray(type, elems, modulo) {
     ta_by_len[i] = items[i] = modulo === false ? i : elems % modulo;
   }
   var ta = new type(items);
-  assert(compareArray([].concat(ta, ta), [ta, ta]));
+  assert(
+    compareArray([].concat(ta, ta), [ta, ta]),
+    'compareArray([].concat(ta, ta), [ta, ta]) must return true'
+  );
   ta[Symbol.isConcatSpreadable] = true;
-  assert(compareArray([].concat(ta), items));
+  assert.compareArray([].concat(ta), items, '[].concat(new type(items)) returns items');
 
-  assert(compareArray([].concat(ta_by_len, ta_by_len), [ta_by_len, ta_by_len]));
+  assert(
+    compareArray([].concat(ta_by_len, ta_by_len), [ta_by_len, ta_by_len]),
+    'compareArray([].concat(ta_by_len, ta_by_len), [ta_by_len, ta_by_len]) must return true'
+  );
   ta_by_len[Symbol.isConcatSpreadable] = true;
-  assert(compareArray([].concat(ta_by_len), items));
+  assert(
+    compareArray([].concat(ta_by_len), items),
+    'compareArray([].concat(ta_by_len), items) must return true'
+  );
 
   // TypedArray with fake `length`.
   ta = new type(1);
@@ -34,7 +43,7 @@ function concatTypedArray(type, elems, modulo) {
     value: 4000
   });
   ta[Symbol.isConcatSpreadable] = true;
-  assert(compareArray([].concat(ta), expected));
+  assert.compareArray([].concat(ta), expected, '[].concat(new type(1)) returns expected');
 }
 var max = [Math.pow(2, 8), Math.pow(2, 16), Math.pow(2, 32), false, false];
 [
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-boolean-wrapper.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-boolean-wrapper.js
index 83c3b9a6ae..b754142a62 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-boolean-wrapper.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-boolean-wrapper.js
@@ -11,25 +11,31 @@ features: [Symbol.isConcatSpreadable]
 ---*/
 var bool = new Boolean(true)
 // Boolean wrapper objects are not concat-spreadable by default
-assert(compareArray([bool], [].concat(bool)));
+assert.compareArray([bool], [].concat(bool), '[bool] must return the same value returned by [].concat(bool)');
 
 // Boolean wrapper objects may be individually concat-spreadable
 bool[Symbol.isConcatSpreadable] = true;
 bool.length = 3;
 bool[0] = 1, bool[1] = 2, bool[2] = 3;
-assert(compareArray([1, 2, 3], [].concat(bool)));
+assert.compareArray([1, 2, 3], [].concat(bool),
+  '[1, 2, 3] must return the same value returned by [].concat(bool)'
+);
 
 Boolean.prototype[Symbol.isConcatSpreadable] = true;
 // Boolean wrapper objects may be concat-spreadable
-assert(compareArray([], [].concat(new Boolean(true))));
+assert.compareArray([], [].concat(new Boolean(true)),
+  '[] must return the same value returned by [].concat(new Boolean(true))'
+);
 Boolean.prototype[0] = 1;
 Boolean.prototype[1] = 2;
 Boolean.prototype[2] = 3;
 Boolean.prototype.length = 3;
-assert(compareArray([1, 2, 3], [].concat(new Boolean(true))));
+assert.compareArray([1, 2, 3], [].concat(new Boolean(true)),
+  '[1, 2, 3] must return the same value returned by [].concat(new Boolean(true))'
+);
 
 // Boolean values are never concat-spreadable
-assert(compareArray([true], [].concat(true)));
+assert.compareArray([true], [].concat(true), '[true] must return the same value returned by [].concat(true)');
 delete Boolean.prototype[Symbol.isConcatSpreadable];
 delete Boolean.prototype[0];
 delete Boolean.prototype[1];
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-function.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-function.js
index 78a55f41e3..e40d44b477 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-function.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-function.js
@@ -11,20 +11,24 @@ features: [Symbol.isConcatSpreadable]
 ---*/
 var fn = function(a, b, c) {}
 // Functions are not concat-spreadable by default
-assert(compareArray([fn], [].concat(fn)));
+assert.compareArray([fn], [].concat(fn), '[fn] must return the same value returned by [].concat(fn)');
 
 // Functions may be individually concat-spreadable
 fn[Symbol.isConcatSpreadable] = true;
 fn[0] = 1, fn[1] = 2, fn[2] = 3;
-assert(compareArray([1, 2, 3], [].concat(fn)));
+assert.compareArray([1, 2, 3], [].concat(fn), '[1, 2, 3] must return the same value returned by [].concat(fn)');
 
 Function.prototype[Symbol.isConcatSpreadable] = true;
 // Functions may be concat-spreadable
-assert(compareArray([void 0, void 0, void 0], [].concat(function(a, b, c) {})));
+assert.compareArray([void 0, void 0, void 0], [].concat(function(a, b, c) {}),
+  '[void 0, void 0, void 0] must return the same value returned by [].concat(function(a, b, c) {})'
+);
 Function.prototype[0] = 1;
 Function.prototype[1] = 2;
 Function.prototype[2] = 3;
-assert(compareArray([1, 2, 3], [].concat(function(a, b, c) {})));
+assert.compareArray([1, 2, 3], [].concat(function(a, b, c) {}),
+  '[1, 2, 3] must return the same value returned by [].concat(function(a, b, c) {})'
+);
 
 delete Function.prototype[Symbol.isConcatSpreadable];
 delete Function.prototype[0];
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-getter-throws.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-getter-throws.js
index 38462cbe5a..971732f6e0 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-getter-throws.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-getter-throws.js
@@ -8,18 +8,17 @@ esid: sec-array.prototype.concat
 description: Array.prototype.concat Symbol.isConcatSpreadable getter throws
 features: [Symbol.isConcatSpreadable]
 ---*/
-function MyError() {}
-var obj = {};
-Object.defineProperty(obj, Symbol.isConcatSpreadable, {
+var spreadablePoisonedGetter = {};
+Object.defineProperty(spreadablePoisonedGetter, Symbol.isConcatSpreadable, {
   get: function() {
-    throw new MyError();
+    throw new Test262Error();
   }
 });
 
-assert.throws(MyError, function() {
-  [].concat(obj);
-});
+assert.throws(Test262Error, function() {
+  [].concat(spreadablePoisonedGetter);
+}, '[].concat(spreadablePoisonedGetter) throws a Test262Error exception');
 
-assert.throws(MyError, function() {
-  Array.prototype.concat.call(obj, 1, 2, 3);
-});
+assert.throws(Test262Error, function() {
+  Array.prototype.concat.call(spreadablePoisonedGetter, 1, 2, 3);
+}, 'Array.prototype.concat.call(spreadablePoisonedGetter, 1, 2, 3) throws a Test262Error exception');
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-number-wrapper.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-number-wrapper.js
index 540de0f36a..62bac94563 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-number-wrapper.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-number-wrapper.js
@@ -11,25 +11,29 @@ features: [Symbol.isConcatSpreadable]
 ---*/
 var num = new Number(true)
 // Number wrapper objects are not concat-spreadable by default
-assert(compareArray([num], [].concat(num)));
+assert.compareArray([num], [].concat(num), '[num] must return the same value returned by [].concat(num)');
 
 // Number wrapper objects may be individually concat-spreadable
 num[Symbol.isConcatSpreadable] = true;
 num.length = 3;
 num[0] = 1, num[1] = 2, num[2] = 3;
-assert(compareArray([1, 2, 3], [].concat(num)));
+assert.compareArray([1, 2, 3], [].concat(num), '[1, 2, 3] must return the same value returned by [].concat(num)');
 
 Number.prototype[Symbol.isConcatSpreadable] = true;
 // Number wrapper objects may be concat-spreadable
-assert(compareArray([], [].concat(new Number(123))));
+assert.compareArray([], [].concat(new Number(123)),
+  '[] must return the same value returned by [].concat(new Number(123))'
+);
 Number.prototype[0] = 1;
 Number.prototype[1] = 2;
 Number.prototype[2] = 3;
 Number.prototype.length = 3;
-assert(compareArray([1, 2, 3], [].concat(new Number(123))));
+assert.compareArray([1, 2, 3], [].concat(new Number(123)),
+  '[1, 2, 3] must return the same value returned by [].concat(new Number(123))'
+);
 
 // Number values are never concat-spreadable
-assert(compareArray([true], [].concat(true)));
+assert.compareArray([true], [].concat(true), '[true] must return the same value returned by [].concat(true)');
 delete Number.prototype[Symbol.isConcatSpreadable];
 delete Number.prototype[0];
 delete Number.prototype[1];
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-reg-exp.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-reg-exp.js
index e399fb389d..7c610ae90a 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-reg-exp.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-reg-exp.js
@@ -11,22 +11,26 @@ features: [Symbol.isConcatSpreadable]
 ---*/
 var re = /abc/;
 // RegExps are not concat-spreadable by default
-assert(compareArray([].concat(re), [re]));
+assert.compareArray([].concat(re), [re], '[].concat(/abc/) must return [re]');
 
 // RegExps may be individually concat-spreadable
 re[Symbol.isConcatSpreadable] = true;
 re[0] = 1, re[1] = 2, re[2] = 3, re.length = 3;
-assert(compareArray([].concat(re), [1, 2, 3]));
+assert.compareArray([].concat(re), [1, 2, 3], '[].concat(/abc/) must return [1, 2, 3]');
 
 // RegExps may be concat-spreadable
 RegExp.prototype[Symbol.isConcatSpreadable] = true;
 RegExp.prototype.length = 3;
 
-assert(compareArray([].concat(/abc/), [void 0, void 0, void 0]));
+assert.compareArray([].concat(/abc/), [void 0, void 0, void 0],
+  '[].concat(/abc/) must return [void 0, void 0, void 0]'
+);
 RegExp.prototype[0] = 1;
 RegExp.prototype[1] = 2;
 RegExp.prototype[2] = 3;
-assert(compareArray([].concat(/abc/), [1, 2, 3]));
+assert.compareArray([].concat(/abc/), [1, 2, 3],
+  '[].concat(/abc/) must return [1, 2, 3]'
+);
 
 delete RegExp.prototype[Symbol.isConcatSpreadable];
 delete RegExp.prototype[0];
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-sparse-object.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-sparse-object.js
index 6afe99d2e3..5666a9e0f1 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-sparse-object.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-sparse-object.js
@@ -13,7 +13,11 @@ var obj = {
   length: 5
 };
 obj[Symbol.isConcatSpreadable] = true;
-assert(compareArray([void 0, void 0, void 0, void 0, void 0], [].concat(obj)));
+assert.compareArray([void 0, void 0, void 0, void 0, void 0], [].concat(obj),
+  '[void 0, void 0, void 0, void 0, void 0] must return the same value returned by [].concat(obj)'
+);
 
 obj.length = 4000;
-assert(compareArray(new Array(4000), [].concat(obj)));
+assert.compareArray(new Array(4000), [].concat(obj),
+  'new Array(4000) must return the same value returned by [].concat(obj)'
+);
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-string-wrapper.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-string-wrapper.js
index 9e44307da9..9b20089ef9 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-string-wrapper.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_spreadable-string-wrapper.js
@@ -11,16 +11,22 @@ features: [Symbol.isConcatSpreadable]
 ---*/
 var str1 = new String("yuck\uD83D\uDCA9")
 // String wrapper objects are not concat-spreadable by default
-assert(compareArray([str1], [].concat(str1)));
+assert.compareArray([str1], [].concat(str1), '[str1] must return the same value returned by [].concat(str1)');
 
 // String wrapper objects may be individually concat-spreadable
 str1[Symbol.isConcatSpreadable] = true;
-assert(compareArray(["y", "u", "c", "k", "\uD83D", "\uDCA9"], [].concat(str1)));
+assert.compareArray(["y", "u", "c", "k", "\uD83D", "\uDCA9"], [].concat(str1),
+  '["y", "u", "c", "k", "uD83D", "uDCA9"] must return the same value returned by [].concat(str1)'
+);
 
 String.prototype[Symbol.isConcatSpreadable] = true;
 // String wrapper objects may be concat-spreadable
-assert(compareArray(["y", "u", "c", "k", "\uD83D", "\uDCA9"], [].concat(new String("yuck\uD83D\uDCA9"))));
+assert.compareArray(["y", "u", "c", "k", "\uD83D", "\uDCA9"], [].concat(new String("yuck\uD83D\uDCA9")),
+  '["y", "u", "c", "k", "uD83D", "uDCA9"] must return the same value returned by [].concat(new String("yuckuD83DuDCA9"))'
+);
 
 // String values are never concat-spreadable
-assert(compareArray(["yuck\uD83D\uDCA9"], [].concat("yuck\uD83D\uDCA9")));
+assert.compareArray(["yuck\uD83D\uDCA9"], [].concat("yuck\uD83D\uDCA9"),
+  '["yuckuD83DuDCA9"] must return the same value returned by [].concat("yuckuD83DuDCA9")'
+);
 delete String.prototype[Symbol.isConcatSpreadable];
diff --git a/test/built-ins/Array/prototype/concat/Array.prototype.concat_strict-arguments.js b/test/built-ins/Array/prototype/concat/Array.prototype.concat_strict-arguments.js
index 16683f7a81..8e5da8060f 100644
--- a/test/built-ins/Array/prototype/concat/Array.prototype.concat_strict-arguments.js
+++ b/test/built-ins/Array/prototype/concat/Array.prototype.concat_strict-arguments.js
@@ -14,9 +14,13 @@ var args = (function(a, b, c) {
   return arguments;
 })(1, 2, 3);
 args[Symbol.isConcatSpreadable] = true;
-assert(compareArray([].concat(args, args), [1, 2, 3, 1, 2, 3]));
+assert.compareArray([].concat(args, args), [1, 2, 3, 1, 2, 3],
+  '[].concat("(function(a, b, c) {"use strict"; return arguments;})(1, 2, 3)", "(function(a, b, c) {"use strict"; return arguments;})(1, 2, 3)") must return [1, 2, 3, 1, 2, 3]'
+);
 
 Object.defineProperty(args, "length", {
   value: 6
 });
-assert(compareArray([].concat(args), [1, 2, 3, void 0, void 0, void 0]));
+assert.compareArray([].concat(args), [1, 2, 3, void 0, void 0, void 0],
+  '[].concat("(function(a, b, c) {"use strict"; return arguments;})(1, 2, 3)") must return [1, 2, 3, void 0, void 0, void 0]'
+);
diff --git a/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T1.js b/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T1.js
index 585e048439..c1f617cace 100644
--- a/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T1.js
+++ b/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T1.js
@@ -18,36 +18,10 @@ var arr = x.concat(y, z);
 
 //CHECK#0
 arr.getClass = Object.prototype.toString;
-if (arr.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#0: var x = new Array(); var y = new Array(0,1); var z = new Array(2,3,4); var arr = x.concat(y,z); arr is Array object. Actual: ' + (arr.getClass()));
-}
-
-//CHECK#1
-if (arr[0] !== 0) {
-  throw new Test262Error('#1: var x = new Array(); var y = new Array(0,1); var z = new Array(2,3,4); var arr = x.concat(y,z); arr[0] === 0. Actual: ' + (arr[0]));
-}
-
-//CHECK#2
-if (arr[1] !== 1) {
-  throw new Test262Error('#2: var x = new Array(); var y = new Array(0,1); var z = new Array(2,3,4); var arr = x.concat(y,z); arr[1] === 1. Actual: ' + (arr[1]));
-}
-
-//CHECK#3
-if (arr[2] !== 2) {
-  throw new Test262Error('#3: var x = new Array(); var y = new Array(0,1); var z = new Array(2,3,4); var arr = x.concat(y,z); arr[2] === 2. Actual: ' + (arr[2]));
-}
-
-//CHECK#4
-if (arr[3] !== 3) {
-  throw new Test262Error('#4: var x = new Array(); var y = new Array(0,1); var z = new Array(2,3,4); var arr = x.concat(y,z); arr[3] === 3. Actual: ' + (arr[3]));
-}
-
-//CHECK#5
-if (arr[4] !== 4) {
-  throw new Test262Error('#5: var x = new Array(); var y = new Array(0,1); var z = new Array(2,3,4); var arr = x.concat(y,z); arr[4] === 4. Actual: ' + (arr[4]));
-}
-
-//CHECK#6
-if (arr.length !== 5) {
-  throw new Test262Error('#6: var x = new Array(); var y = new Array(0,1); var z = new Array(2,3,4); var arr = x.concat(y,z); arr.length === 5. Actual: ' + (arr.length));
-}
+assert.sameValue(arr.getClass(), "[object Array]", 'arr.getClass() must return "[object Array]"');
+assert.sameValue(arr[0], 0, 'The value of arr[0] is expected to be 0');
+assert.sameValue(arr[1], 1, 'The value of arr[1] is expected to be 1');
+assert.sameValue(arr[2], 2, 'The value of arr[2] is expected to be 2');
+assert.sameValue(arr[3], 3, 'The value of arr[3] is expected to be 3');
+assert.sameValue(arr[4], 4, 'The value of arr[4] is expected to be 4');
+assert.sameValue(arr.length, 5, 'The value of arr.length is expected to be 5');
diff --git a/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T2.js b/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T2.js
index a425e98283..3a095865ef 100644
--- a/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T2.js
+++ b/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T2.js
@@ -18,46 +18,12 @@ var arr = x.concat(y, z, -1, true, "NaN");
 
 //CHECK#0
 arr.getClass = Object.prototype.toString;
-if (arr.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#0: var x = [0]; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr is Array object. Actual: ' + (arr.getClass()));
-}
-
-//CHECK#1
-if (arr[0] !== 0) {
-  throw new Test262Error('#1: var x = [0]; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[0] === 0. Actual: ' + (arr[0]));
-}
-
-//CHECK#2
-if (arr[1] !== y) {
-  throw new Test262Error('#2: var x = [0]; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[1] === y. Actual: ' + (arr[1]));
-}
-
-//CHECK#3
-if (arr[2] !== 1) {
-  throw new Test262Error('#3: var x = [0]; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[2] === 1. Actual: ' + (arr[2]));
-}
-
-//CHECK#4
-if (arr[3] !== 2) {
-  throw new Test262Error('#4: var x = [0]; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[3] === 2. Actual: ' + (arr[3]));
-}
-
-//CHECK#5
-if (arr[4] !== -1) {
-  throw new Test262Error('#5: var x = [0]; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[4] === -1. Actual: ' + (arr[4]));
-}
-
-//CHECK#6
-if (arr[5] !== true) {
-  throw new Test262Error('#6: var x = [0]; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[5] === true. Actual: ' + (arr[5]));
-}
-
-//CHECK#7
-if (arr[6] !== "NaN") {
-  throw new Test262Error('#7: var x = [0]; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[6] === "NaN". Actual: ' + (arr[6]));
-}
-
-//CHECK#8
-if (arr.length !== 7) {
-  throw new Test262Error('#8: var x = [0]; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr.length === 7. Actual: ' + (arr.length));
-}
+assert.sameValue(arr.getClass(), "[object Array]", 'arr.getClass() must return "[object Array]"');
+assert.sameValue(arr[0], 0, 'The value of arr[0] is expected to be 0');
+assert.sameValue(arr[1], y, 'The value of arr[1] is expected to equal the value of y');
+assert.sameValue(arr[2], 1, 'The value of arr[2] is expected to be 1');
+assert.sameValue(arr[3], 2, 'The value of arr[3] is expected to be 2');
+assert.sameValue(arr[4], -1, 'The value of arr[4] is expected to be -1');
+assert.sameValue(arr[5], true, 'The value of arr[5] is expected to be true');
+assert.sameValue(arr[6], "NaN", 'The value of arr[6] is expected to be "NaN"');
+assert.sameValue(arr.length, 7, 'The value of arr.length is expected to be 7');
diff --git a/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T3.js b/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T3.js
index 08c6d5e62a..5331193a6c 100644
--- a/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T3.js
+++ b/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T3.js
@@ -16,26 +16,8 @@ var arr = x.concat();
 
 //CHECK#0
 arr.getClass = Object.prototype.toString;
-if (arr.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#0: var x = [0,1]; var arr = x.concat(); arr is Array object. Actual: ' + (arr.getClass()));
-}
-
-//CHECK#1
-if (arr[0] !== 0) {
-  throw new Test262Error('#1: var x = [0,1]; var arr = x.concat(); arr[0] === 0. Actual: ' + (arr[0]));
-}
-
-//CHECK#2
-if (arr[1] !== 1) {
-  throw new Test262Error('#2: var x = [0,1]; var arr = x.concat(); arr[1] === 1. Actual: ' + (arr[1]));
-}
-
-//CHECK#3
-if (arr.length !== 2) {
-  throw new Test262Error('#3: var x = [0,1]; var arr = x.concat(); arr.length === 2. Actual: ' + (arr.length));
-}
-
-//CHECK#4
-if (arr === x) {
-  throw new Test262Error('#4: var x = [0,1]; var arr = x.concat(); arr !== x');
-}
+assert.sameValue(arr.getClass(), "[object Array]", 'arr.getClass() must return "[object Array]"');
+assert.sameValue(arr[0], 0, 'The value of arr[0] is expected to be 0');
+assert.sameValue(arr[1], 1, 'The value of arr[1] is expected to be 1');
+assert.sameValue(arr.length, 2, 'The value of arr.length is expected to be 2');
+assert.notSameValue(arr, x, 'The value of arr is expected to not equal the value of `x`');
diff --git a/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T4.js b/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T4.js
index 4700fbe871..082cc4a236 100644
--- a/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T4.js
+++ b/test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T4.js
@@ -16,26 +16,8 @@ var arr = x.concat([], [, ]);
 
 //CHECK#0
 arr.getClass = Object.prototype.toString;
-if (arr.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#0: var x = [,1]; var arr = x.concat([], [,]); arr is Array object. Actual: ' + (arr.getClass()));
-}
-
-//CHECK#1
-if (arr[0] !== undefined) {
-  throw new Test262Error('#1: var x = [,1]; var arr = x.concat([], [,]); arr[0] === undefined. Actual: ' + (arr[0]));
-}
-
-//CHECK#2
-if (arr[1] !== 1) {
-  throw new Test262Error('#2: var x = [,1]; var arr = x.concat([], [,]); arr[1] === 1. Actual: ' + (arr[1]));
-}
-
-//CHECK#2
-if (arr[2] !== undefined) {
-  throw new Test262Error('#2: var x = [,1]; var arr = x.concat([], [,]); arr[2] === undefined. Actual: ' + (arr[2]));
-}
-
-//CHECK#4
-if (arr.length !== 3) {
-  throw new Test262Error('#4: var x = [,1]; var arr = x.concat([], [,]); arr.length === 3. Actual: ' + (arr.length));
-}
+assert.sameValue(arr.getClass(), "[object Array]", 'arr.getClass() must return "[object Array]"');
+assert.sameValue(arr[0], undefined, 'The value of arr[0] is expected to equal undefined');
+assert.sameValue(arr[1], 1, 'The value of arr[1] is expected to be 1');
+assert.sameValue(arr[2], undefined, 'The value of arr[2] is expected to equal undefined');
+assert.sameValue(arr.length, 3, 'The value of arr.length is expected to be 3');
diff --git a/test/built-ins/Array/prototype/concat/S15.4.4.4_A2_T1.js b/test/built-ins/Array/prototype/concat/S15.4.4.4_A2_T1.js
index 5f4ae0e313..aedd191070 100644
--- a/test/built-ins/Array/prototype/concat/S15.4.4.4_A2_T1.js
+++ b/test/built-ins/Array/prototype/concat/S15.4.4.4_A2_T1.js
@@ -18,46 +18,12 @@ var arr = x.concat(y, z, -1, true, "NaN");
 
 //CHECK#0
 arr.getClass = Object.prototype.toString;
-if (arr.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#0: var x = {}; x.concat = Array.prototype.concat; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr is Array object. Actual: ' + (arr.getClass()));
-}
-
-//CHECK#1
-if (arr[0] !== x) {
-  throw new Test262Error('#1: var x = {}; x.concat = Array.prototype.concat; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[0] === x. Actual: ' + (arr[0]));
-}
-
-//CHECK#2
-if (arr[1] !== y) {
-  throw new Test262Error('#2: var x = {}; x.concat = Array.prototype.concat; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[1] === y. Actual: ' + (arr[1]));
-}
-
-//CHECK#3
-if (arr[2] !== 1) {
-  throw new Test262Error('#3: var x = {}; x.concat = Array.prototype.concat; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[2] === 1. Actual: ' + (arr[2]));
-}
-
-//CHECK#4
-if (arr[3] !== 2) {
-  throw new Test262Error('#4: var x = {}; x.concat = Array.prototype.concat; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[3] === 2. Actual: ' + (arr[3]));
-}
-
-//CHECK#5
-if (arr[4] !== -1) {
-  throw new Test262Error('#5: var x = {}; x.concat = Array.prototype.concat; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[4] === -1. Actual: ' + (arr[4]));
-}
-
-//CHECK#6
-if (arr[5] !== true) {
-  throw new Test262Error('#6: var x = {}; x.concat = Array.prototype.concat; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[5] === true. Actual: ' + (arr[5]));
-}
-
-//CHECK#7
-if (arr[6] !== "NaN") {
-  throw new Test262Error('#7: var x = {}; x.concat = Array.prototype.concat; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr[6] === "NaN". Actual: ' + (arr[6]));
-}
-
-//CHECK#8
-if (arr.length !== 7) {
-  throw new Test262Error('#8: var x = {}; x.concat = Array.prototype.concat; var y = new Object(); var z = new Array(1,2); var arr = x.concat(y,z, -1, true, "NaN"); arr.length === 7. Actual: ' + (arr.length));
-}
+assert.sameValue(arr.getClass(), "[object Array]", 'arr.getClass() must return "[object Array]"');
+assert.sameValue(arr[0], x, 'The value of arr[0] is expected to equal the value of x');
+assert.sameValue(arr[1], y, 'The value of arr[1] is expected to equal the value of y');
+assert.sameValue(arr[2], 1, 'The value of arr[2] is expected to be 1');
+assert.sameValue(arr[3], 2, 'The value of arr[3] is expected to be 2');
+assert.sameValue(arr[4], -1, 'The value of arr[4] is expected to be -1');
+assert.sameValue(arr[5], true, 'The value of arr[5] is expected to be true');
+assert.sameValue(arr[6], "NaN", 'The value of arr[6] is expected to be "NaN"');
+assert.sameValue(arr.length, 7, 'The value of arr.length is expected to be 7');
diff --git a/test/built-ins/Array/prototype/concat/S15.4.4.4_A2_T2.js b/test/built-ins/Array/prototype/concat/S15.4.4.4_A2_T2.js
index 73f05eda8a..3d172ac6ed 100644
--- a/test/built-ins/Array/prototype/concat/S15.4.4.4_A2_T2.js
+++ b/test/built-ins/Array/prototype/concat/S15.4.4.4_A2_T2.js
@@ -16,16 +16,6 @@ var arr = x.concat();
 
 //CHECK#0
 arr.getClass = Object.prototype.toString;
-if (arr.getClass() !== "[object " + "Array" + "]") {
-  throw new Test262Error('#0: var x = {}; x.concat = Array.prototype.concat; var arr = x.concat() arr is Array object. Actual: ' + (arr.getClass()));
-}
-
-//CHECK#1
-if (arr[0] !== x) {
-  throw new Test262Error('#1: var x = {}; x.concat = Array.prototype.concat; var arr = x.concat(); arr[0] === x. Actual: ' + (arr[0]));
-}
-
-//CHECK#2
-if (arr.length !== 1) {
-  throw new Test262Error('#2: var x = {}; x.concat = Array.prototype.concat; var arr = x.concat(); arr.length === 1. Actual: ' + (arr.length));
-}
+assert.sameValue(arr.getClass(), "[object Array]", 'arr.getClass() must return "[object Array]"');
+assert.sameValue(arr[0], x, 'The value of arr[0] is expected to equal the value of x');
+assert.sameValue(arr.length, 1, 'The value of arr.length is expected to be 1');
diff --git a/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T1.js b/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T1.js
index 81ba10d44e..b07baf3387 100644
--- a/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T1.js
+++ b/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T1.js
@@ -15,20 +15,9 @@ var x = [0];
 x.length = 2;
 var arr = x.concat();
 
-//CHECK#1
-if (arr[0] !== 0) {
-  throw new Test262Error('#1: Array.prototype[1] = 1; x = [0]; x.length = 2; var arr = x.concat(); arr[0] === 0. Actual: ' + (arr[0]));
-}
-
-//CHECK#2
-if (arr[1] !== 1) {
-  throw new Test262Error('#2: Array.prototype[1] = 1; x = [0]; x.length = 2; var arr = x.concat(); arr[1] === 1. Actual: ' + (arr[1]));
-}
-
-//CHECK#3
-if (arr.hasOwnProperty('1') !== true) {
-  throw new Test262Error('#3: Array.prototype[1] = 1; x = [0]; x.length = 2; var arr = x.concat(); arr.hasOwnProperty(\'1\') === true. Actual: ' + (arr.hasOwnProperty('1')));
-}
+assert.sameValue(arr[0], 0, 'The value of arr[0] is expected to be 0');
+assert.sameValue(arr[1], 1, 'The value of arr[1] is expected to be 1');
+assert.sameValue(arr.hasOwnProperty('1'), true, 'arr.hasOwnProperty("1") must return true');
 
 Object.prototype[1] = 1;
 Object.prototype.length = 2;
@@ -38,17 +27,6 @@ x = {
 };
 var arr = x.concat();
 
-//CHECK#4
-if (arr[0] !== x) {
-  throw new Test262Error('#4: Object.prototype[1] = 1; Object.prototype.length = 2; Object.prototype.concat = Array.prototype.concat; x = {0:0}; var arr = x.concat(); arr[0] === x. Actual: ' + (arr[0]));
-}
-
-//CHECK#5
-if (arr[1] !== 1) {
-  throw new Test262Error('#5: Object.prototype[1] = 1; Object.prototype.length = 2; Object.prototype.concat = Array.prototype.concat; x = {0:0}; var arr = x.concat(); arr[1] === 1. Actual: ' + (arr[1]));
-}
-
-//CHECK#6
-if (arr.hasOwnProperty('1') !== false) {
-  throw new Test262Error('#6: Object.prototype[1] = 1; Object.prototype.length = 2; Object.prototype.concat = Array.prototype.concat; x = {0:0}; var arr = x.concat(); arr.hasOwnProperty(\'1\') === false. Actual: ' + (arr.hasOwnProperty('1')));
-}
+assert.sameValue(arr[0], x, 'The value of arr[0] is expected to equal the value of x');
+assert.sameValue(arr[1], 1, 'The value of arr[1] is expected to be 1');
+assert.sameValue(arr.hasOwnProperty('1'), false, 'arr.hasOwnProperty("1") must return false');
diff --git a/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T2.js b/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T2.js
index fd975863c8..e274c05984 100644
--- a/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T2.js
+++ b/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T2.js
@@ -11,54 +11,25 @@ description: >
 
 var a = [0];
 
-if (a.length !== 1) {
-  throw new Test262Error("expected a.length === 1, actually " + a.length);
-}
+assert.sameValue(a.length, 1, 'The value of a.length is expected to be 1');
 
 a.length = 3;
 
-if (a[1] !== undefined) {
-  throw new Test262Error("expected a[1] === undefined, actually " + a[1]);
-}
-if (a[2] !== undefined) {
-  throw new Test262Error("expected a[2] === undefined, actually " + a[2]);
-}
+assert.sameValue(a[1], undefined, 'The value of a[1] is expected to equal undefined');
+assert.sameValue(a[2], undefined, 'The value of a[2] is expected to equal undefined');
 
 Array.prototype[2] = 2;
 
-if (a[1] !== undefined) {
-  throw new Test262Error("expected a[1] === undefined, actually " + a[1]);
-}
-if (a[2] !== 2) {
-  throw new Test262Error("expected a[2] === 2, actually " + a[2]);
-}
-
-if (a.hasOwnProperty('1') !== false) {
-  throw new Test262Error("a.hasOwnProperty('1') === false, actually " + a.hasOwnProperty('1'));
-}
-if (a.hasOwnProperty('2') !== false) {
-  throw new Test262Error("a.hasOwnProperty('2') === false, actually " + a.hasOwnProperty('2'));
-}
+assert.sameValue(a[1], undefined, 'The value of a[1] is expected to equal undefined');
+assert.sameValue(a[2], 2, 'The value of a[2] is expected to be 2');
+assert.sameValue(a.hasOwnProperty('1'), false, 'a.hasOwnProperty("1") must return false');
+assert.sameValue(a.hasOwnProperty('2'), false, 'a.hasOwnProperty("2") must return false');
 
 var b = a.concat();
 
-if (b.length !== 3) {
-  throw new Test262Error("expected b.length === 3, actually " + b.length);
-}
-
-if (b[0] !== 0) {
-  throw new Test262Error("expected b[0] === 0, actually " + b[0]);
-}
-if (b[1] !== undefined) {
-  throw new Test262Error("expected b[1] === undefined, actually " + b[1]);
-}
-if (b[2] !== 2) {
-  throw new Test262Error("expected b[2] === 2, actually " + b[2]);
-}
-
-if (b.hasOwnProperty('1') !== false) {
-  throw new Test262Error("expected b.hasOwnProperty('1') === false, actually " + b.hasOwnProperty('1'));
-}
-if (b.hasOwnProperty('2') !== true) {
-  throw new Test262Error("expected b.hasOwnProperty('2') === true, actually " + b.hasOwnProperty('2'));
-}
+assert.sameValue(b.length, 3, 'The value of b.length is expected to be 3');
+assert.sameValue(b[0], 0, 'The value of b[0] is expected to be 0');
+assert.sameValue(b[1], undefined, 'The value of b[1] is expected to equal undefined');
+assert.sameValue(b[2], 2, 'The value of b[2] is expected to be 2');
+assert.sameValue(b.hasOwnProperty('1'), false, 'b.hasOwnProperty("1") must return false');
+assert.sameValue(b.hasOwnProperty('2'), true, 'b.hasOwnProperty("2") must return true');
diff --git a/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T3.js b/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T3.js
index 75f0f99aba..12d6525839 100644
--- a/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T3.js
+++ b/test/built-ins/Array/prototype/concat/S15.4.4.4_A3_T3.js
@@ -11,54 +11,25 @@ description: >
 
 var a = [0];
 
-if (a.length !== 1) {
-  throw new Test262Error("expected a.length === 1, actually " + a.length);
-}
+assert.sameValue(a.length, 1, 'The value of a.length is expected to be 1');
 
 a.length = 3;
 
-if (a[1] !== undefined) {
-  throw new Test262Error("expected a[1] === undefined, actually " + a[1]);
-}
-if (a[2] !== undefined) {
-  throw new Test262Error("expected a[2] === undefined, actually " + a[2]);
-}
+assert.sameValue(a[1], undefined, 'The value of a[1] is expected to equal undefined');
+assert.sameValue(a[2], undefined, 'The value of a[2] is expected to equal undefined');
 
 Object.prototype[2] = 2;
 
-if (a[1] !== undefined) {
-  throw new Test262Error("expected a[1] === undefined, actually " + a[1]);
-}
-if (a[2] !== 2) {
-  throw new Test262Error("expected a[2] === 2, actually " + a[2]);
-}
-
-if (a.hasOwnProperty('1') !== false) {
-  throw new Test262Error("a.hasOwnProperty('1') === false, actually " + a.hasOwnProperty('1'));
-}
-if (a.hasOwnProperty('2') !== false) {
-  throw new Test262Error("a.hasOwnProperty('2') === false, actually " + a.hasOwnProperty('2'));
-}
+assert.sameValue(a[1], undefined, 'The value of a[1] is expected to equal undefined');
+assert.sameValue(a[2], 2, 'The value of a[2] is expected to be 2');
+assert.sameValue(a.hasOwnProperty('1'), false, 'a.hasOwnProperty("1") must return false');
+assert.sameValue(a.hasOwnProperty('2'), false, 'a.hasOwnProperty("2") must return false');
 
 var b = a.concat();
 
-if (b.length !== 3) {
-  throw new Test262Error("expected b.length === 3, actually " + b.length);
-}
-
-if (b[0] !== 0) {
-  throw new Test262Error("expected b[0] === 0, actually " + b[0]);
-}
-if (b[1] !== undefined) {
-  throw new Test262Error("expected b[1] === undefined, actually " + b[1]);
-}
-if (b[2] !== 2) {
-  throw new Test262Error("expected b[2] === 2, actually " + b[2]);
-}
-
-if (b.hasOwnProperty('1') !== false) {
-  throw new Test262Error("expected b.hasOwnProperty('1') === false, actually " + b.hasOwnProperty('1'));
-}
-if (b.hasOwnProperty('2') !== true) {
-  throw new Test262Error("expected b.hasOwnProperty('2') === true, actually " + b.hasOwnProperty('2'));
-}
+assert.sameValue(b.length, 3, 'The value of b.length is expected to be 3');
+assert.sameValue(b[0], 0, 'The value of b[0] is expected to be 0');
+assert.sameValue(b[1], undefined, 'The value of b[1] is expected to equal undefined');
+assert.sameValue(b[2], 2, 'The value of b[2] is expected to be 2');
+assert.sameValue(b.hasOwnProperty('1'), false, 'b.hasOwnProperty("1") must return false');
+assert.sameValue(b.hasOwnProperty('2'), true, 'b.hasOwnProperty("2") must return true');
diff --git a/test/built-ins/Array/prototype/concat/arg-length-exceeding-integer-limit.js b/test/built-ins/Array/prototype/concat/arg-length-exceeding-integer-limit.js
index 6c0f56b9a1..814259b3ed 100644
--- a/test/built-ins/Array/prototype/concat/arg-length-exceeding-integer-limit.js
+++ b/test/built-ins/Array/prototype/concat/arg-length-exceeding-integer-limit.js
@@ -19,15 +19,15 @@ info: |
 features: [Symbol.isConcatSpreadable, Proxy]
 ---*/
 
-var spreadable = {};
-spreadable.length = Number.MAX_SAFE_INTEGER;
-spreadable[Symbol.isConcatSpreadable] = true;
+var spreadableLengthOutOfRange = {};
+spreadableLengthOutOfRange.length = Number.MAX_SAFE_INTEGER;
+spreadableLengthOutOfRange[Symbol.isConcatSpreadable] = true;
 
 assert.throws(TypeError, function() {
-  [1].concat(spreadable);
-});
+  [1].concat(spreadableLengthOutOfRange);
+}, '[1].concat(spreadableLengthOutOfRange) throws a TypeError exception');
 
-var proxy = new Proxy([], {
+var proxyForArrayWithLengthOutOfRange = new Proxy([], {
   get: function(_target, key) {
     if (key === "length") {
       return Number.MAX_SAFE_INTEGER;
@@ -36,5 +36,5 @@ var proxy = new Proxy([], {
 });
 
 assert.throws(TypeError, function() {
-  [].concat(1, proxy);
-});
+  [].concat(1, proxyForArrayWithLengthOutOfRange);
+}, '[].concat(1, proxyForArrayWithLengthOutOfRange) throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/concat/arg-length-near-integer-limit.js b/test/built-ins/Array/prototype/concat/arg-length-near-integer-limit.js
index 9321c5a139..9c6e154229 100644
--- a/test/built-ins/Array/prototype/concat/arg-length-near-integer-limit.js
+++ b/test/built-ins/Array/prototype/concat/arg-length-near-integer-limit.js
@@ -24,14 +24,14 @@ info: |
 features: [Symbol.isConcatSpreadable]
 ---*/
 
-var spreadable = {
+var spreadableHasPoisonedIndex = {
   length: Number.MAX_SAFE_INTEGER,
   get 0() {
     throw new Test262Error();
   },
 };
-spreadable[Symbol.isConcatSpreadable] = true;
+spreadableHasPoisonedIndex[Symbol.isConcatSpreadable] = true;
 
 assert.throws(Test262Error, function() {
-  [].concat(spreadable);
-});
+  [].concat(spreadableHasPoisonedIndex);
+}, '[].concat(spreadableHasPoisonedIndex) throws a Test262Error exception');
diff --git a/test/built-ins/Array/prototype/concat/call-with-boolean.js b/test/built-ins/Array/prototype/concat/call-with-boolean.js
index 9e4fe4a8a2..6165d185b1 100644
--- a/test/built-ins/Array/prototype/concat/call-with-boolean.js
+++ b/test/built-ins/Array/prototype/concat/call-with-boolean.js
@@ -9,10 +9,10 @@ description: Array.prototype.concat applied to boolean primitive
 assert.sameValue(
   Array.prototype.concat.call(true)[0] instanceof Boolean,
   true,
-  'The result of `(Array.prototype.concat.call(true)[0] instanceof Boolean)` is true'
+  'The result of evaluating (Array.prototype.concat.call(true)[0] instanceof Boolean) is expected to be true'
 );
 assert.sameValue(
   Array.prototype.concat.call(false)[0] instanceof Boolean,
   true,
-  'The result of `(Array.prototype.concat.call(false)[0] instanceof Boolean)` is true'
+  'The result of evaluating (Array.prototype.concat.call(false)[0] instanceof Boolean) is expected to be true'
 );
diff --git a/test/built-ins/Array/prototype/concat/create-ctor-non-object.js b/test/built-ins/Array/prototype/concat/create-ctor-non-object.js
index e1570411c8..19b56ba825 100644
--- a/test/built-ins/Array/prototype/concat/create-ctor-non-object.js
+++ b/test/built-ins/Array/prototype/concat/create-ctor-non-object.js
@@ -21,22 +21,22 @@ var a = [];
 a.constructor = null;
 assert.throws(TypeError, function() {
   a.concat();
-}, 'null value');
+}, 'a.concat() throws a TypeError exception');
 
 a = [];
 a.constructor = 1;
 assert.throws(TypeError, function() {
   a.concat();
-}, 'number value');
+}, 'a.concat() throws a TypeError exception');
 
 a = [];
 a.constructor = 'string';
 assert.throws(TypeError, function() {
   a.concat();
-}, 'string value');
+}, 'a.concat() throws a TypeError exception');
 
 a = [];
 a.constructor = true;
 assert.throws(TypeError, function() {
   a.concat();
-}, 'boolean value');
+}, 'a.concat() throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/concat/create-ctor-poisoned.js b/test/built-ins/Array/prototype/concat/create-ctor-poisoned.js
index d8a87ab249..63599b9d2d 100644
--- a/test/built-ins/Array/prototype/concat/create-ctor-poisoned.js
+++ b/test/built-ins/Array/prototype/concat/create-ctor-poisoned.js
@@ -23,4 +23,4 @@ Object.defineProperty(a, 'constructor', {
 
 assert.throws(Test262Error, function() {
   a.concat();
-});
+}, 'a.concat() throws a Test262Error exception');
diff --git a/test/built-ins/Array/prototype/concat/create-non-array.js b/test/built-ins/Array/prototype/concat/create-non-array.js
index dfb8f18f16..0a4765e69e 100644
--- a/test/built-ins/Array/prototype/concat/create-non-array.js
+++ b/test/built-ins/Array/prototype/concat/create-non-array.js
@@ -27,8 +27,12 @@ Object.defineProperty(obj, 'constructor', {
 
 result = Array.prototype.concat.call(obj);
 
-assert.sameValue(callCount, 0, '`constructor` property not accessed');
-assert.sameValue(Object.getPrototypeOf(result), Array.prototype);
-assert(Array.isArray(result), 'result is an Array exotic object');
-assert.sameValue(result.length, 1, 'array created with appropriate length');
-assert.sameValue(result[0], obj);
+assert.sameValue(callCount, 0, 'The value of callCount is expected to be 0');
+assert.sameValue(
+  Object.getPrototypeOf(result),
+  Array.prototype,
+  'Object.getPrototypeOf(Array.prototype.concat.call(obj)) returns Array.prototype'
+);
+assert(Array.isArray(result), 'Array.isArray(result) must return true');
+assert.sameValue(result.length, 1, 'The value of result.length is expected to be 1');
+assert.sameValue(result[0], obj, 'The value of result[0] is expected to equal the value of obj');
diff --git a/test/built-ins/Array/prototype/concat/create-proto-from-ctor-realm-array.js b/test/built-ins/Array/prototype/concat/create-proto-from-ctor-realm-array.js
index 6a9ddc9b6b..fc9915ae1a 100644
--- a/test/built-ins/Array/prototype/concat/create-proto-from-ctor-realm-array.js
+++ b/test/built-ins/Array/prototype/concat/create-proto-from-ctor-realm-array.js
@@ -38,5 +38,9 @@ Object.defineProperty(OArray, Symbol.species, speciesDesc);
 
 result = array.concat();
 
-assert.sameValue(Object.getPrototypeOf(result), Array.prototype);
-assert.sameValue(callCount, 0, 'Species constructor is not referenced');
+assert.sameValue(
+  Object.getPrototypeOf(result),
+  Array.prototype,
+  'Object.getPrototypeOf(array.concat()) returns Array.prototype'
+);
+assert.sameValue(callCount, 0, 'The value of callCount is expected to be 0');
diff --git a/test/built-ins/Array/prototype/concat/create-proto-from-ctor-realm-non-array.js b/test/built-ins/Array/prototype/concat/create-proto-from-ctor-realm-non-array.js
index e3aef0fd8c..002a606941 100644
--- a/test/built-ins/Array/prototype/concat/create-proto-from-ctor-realm-non-array.js
+++ b/test/built-ins/Array/prototype/concat/create-proto-from-ctor-realm-non-array.js
@@ -39,5 +39,9 @@ Object.defineProperty(Array, Symbol.species, speciesDesc);
 
 result = array.concat();
 
-assert.sameValue(Object.getPrototypeOf(result), CustomCtor.prototype);
-assert.sameValue(callCount, 0, 'Array species constructor is not referenced');
+assert.sameValue(
+  Object.getPrototypeOf(result),
+  CustomCtor.prototype,
+  'Object.getPrototypeOf(array.concat()) returns CustomCtor.prototype'
+);
+assert.sameValue(callCount, 0, 'The value of callCount is expected to be 0');
diff --git a/test/built-ins/Array/prototype/concat/create-proxy.js b/test/built-ins/Array/prototype/concat/create-proxy.js
index 93e1d57e78..9475ddc2b5 100644
--- a/test/built-ins/Array/prototype/concat/create-proxy.js
+++ b/test/built-ins/Array/prototype/concat/create-proxy.js
@@ -36,4 +36,8 @@ array.constructor[Symbol.species] = Ctor;
 
 result = Array.prototype.concat.call(proxy);
 
-assert.sameValue(Object.getPrototypeOf(result), Ctor.prototype);
+assert.sameValue(
+  Object.getPrototypeOf(result),
+  Ctor.prototype,
+  'Object.getPrototypeOf(Array.prototype.concat.call(proxy)) returns Ctor.prototype'
+);
diff --git a/test/built-ins/Array/prototype/concat/create-revoked-proxy.js b/test/built-ins/Array/prototype/concat/create-revoked-proxy.js
index d7a09b7c7f..4fd0716526 100644
--- a/test/built-ins/Array/prototype/concat/create-revoked-proxy.js
+++ b/test/built-ins/Array/prototype/concat/create-revoked-proxy.js
@@ -33,6 +33,6 @@ o.revoke();
 
 assert.throws(TypeError, function() {
   Array.prototype.concat.call(o.proxy);
-});
+}, 'Array.prototype.concat.call(o.proxy) throws a TypeError exception');
 
-assert.sameValue(callCount, 0, '`constructor` property not accessed');
+assert.sameValue(callCount, 0, 'The value of callCount is expected to be 0');
diff --git a/test/built-ins/Array/prototype/concat/create-species-abrupt.js b/test/built-ins/Array/prototype/concat/create-species-abrupt.js
index bd5649983b..cf7fc3de80 100644
--- a/test/built-ins/Array/prototype/concat/create-species-abrupt.js
+++ b/test/built-ins/Array/prototype/concat/create-species-abrupt.js
@@ -29,4 +29,4 @@ a.constructor[Symbol.species] = Ctor;
 
 assert.throws(Test262Error, function() {
   a.concat();
-});
+}, 'a.concat() throws a Test262Error exception');
diff --git a/test/built-ins/Array/prototype/concat/create-species-non-ctor.js b/test/built-ins/Array/prototype/concat/create-species-non-ctor.js
index 00ff522d06..1095078be4 100644
--- a/test/built-ins/Array/prototype/concat/create-species-non-ctor.js
+++ b/test/built-ins/Array/prototype/concat/create-species-non-ctor.js
@@ -28,4 +28,4 @@ a.constructor[Symbol.species] = parseInt;
 
 assert.throws(TypeError, function() {
   a.concat();
-});
+}, 'a.concat() throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/concat/create-species-non-extensible-spreadable.js b/test/built-ins/Array/prototype/concat/create-species-non-extensible-spreadable.js
index 1565025e40..3fb74440fe 100644
--- a/test/built-ins/Array/prototype/concat/create-species-non-extensible-spreadable.js
+++ b/test/built-ins/Array/prototype/concat/create-species-non-extensible-spreadable.js
@@ -40,4 +40,4 @@ arr.constructor[Symbol.species] = A;
 
 assert.throws(TypeError, function() {
   arr.concat([1]);
-});
+}, 'arr.concat([1]) throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/concat/create-species-non-extensible.js b/test/built-ins/Array/prototype/concat/create-species-non-extensible.js
index ce69c532ef..5ee7bba247 100644
--- a/test/built-ins/Array/prototype/concat/create-species-non-extensible.js
+++ b/test/built-ins/Array/prototype/concat/create-species-non-extensible.js
@@ -38,4 +38,4 @@ arr.constructor[Symbol.species] = A;
 
 assert.throws(TypeError, function() {
   arr.concat(1);
-});
+}, 'arr.concat(1) throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/concat/create-species-null.js b/test/built-ins/Array/prototype/concat/create-species-null.js
index a53bee3331..ab7cbdbe6e 100644
--- a/test/built-ins/Array/prototype/concat/create-species-null.js
+++ b/test/built-ins/Array/prototype/concat/create-species-null.js
@@ -28,5 +28,9 @@ a.constructor[Symbol.species] = null;
 
 result = a.concat();
 
-assert.sameValue(Object.getPrototypeOf(result), Array.prototype);
-assert(Array.isArray(result), 'result is an Array exotic object');
+assert.sameValue(
+  Object.getPrototypeOf(result),
+  Array.prototype,
+  'Object.getPrototypeOf(a.concat()) returns Array.prototype'
+);
+assert(Array.isArray(result), 'Array.isArray(result) must return true');
diff --git a/test/built-ins/Array/prototype/concat/create-species-poisoned.js b/test/built-ins/Array/prototype/concat/create-species-poisoned.js
index 174ee3dfe5..aecbe9a2f6 100644
--- a/test/built-ins/Array/prototype/concat/create-species-poisoned.js
+++ b/test/built-ins/Array/prototype/concat/create-species-poisoned.js
@@ -28,4 +28,4 @@ Object.defineProperty(a.constructor, Symbol.species, {
 
 assert.throws(Test262Error, function() {
   a.concat();
-});
+}, 'a.concat() throws a Test262Error exception');
diff --git a/test/built-ins/Array/prototype/concat/create-species-undef.js b/test/built-ins/Array/prototype/concat/create-species-undef.js
index 129945ae00..dda56e5b25 100644
--- a/test/built-ins/Array/prototype/concat/create-species-undef.js
+++ b/test/built-ins/Array/prototype/concat/create-species-undef.js
@@ -30,5 +30,9 @@ a.constructor[Symbol.species] = undefined;
 
 result = a.concat();
 
-assert.sameValue(Object.getPrototypeOf(result), Array.prototype);
-assert(Array.isArray(result), 'result is an Array exotic object');
+assert.sameValue(
+  Object.getPrototypeOf(result),
+  Array.prototype,
+  'Object.getPrototypeOf(a.concat()) returns Array.prototype'
+);
+assert(Array.isArray(result), 'Array.isArray(result) must return true');
diff --git a/test/built-ins/Array/prototype/concat/create-species-with-non-configurable-property-spreadable.js b/test/built-ins/Array/prototype/concat/create-species-with-non-configurable-property-spreadable.js
index 6ae665eca5..f86e16f2c2 100644
--- a/test/built-ins/Array/prototype/concat/create-species-with-non-configurable-property-spreadable.js
+++ b/test/built-ins/Array/prototype/concat/create-species-with-non-configurable-property-spreadable.js
@@ -42,4 +42,4 @@ arr.constructor[Symbol.species] = A;
 
 assert.throws(TypeError, function() {
   arr.concat([1]);
-});
+}, 'arr.concat([1]) throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/concat/create-species-with-non-configurable-property.js b/test/built-ins/Array/prototype/concat/create-species-with-non-configurable-property.js
index bf3eb73b5f..cb2b5fda16 100644
--- a/test/built-ins/Array/prototype/concat/create-species-with-non-configurable-property.js
+++ b/test/built-ins/Array/prototype/concat/create-species-with-non-configurable-property.js
@@ -40,4 +40,4 @@ arr.constructor[Symbol.species] = A;
 
 assert.throws(TypeError, function() {
   arr.concat(1);
-});
+}, 'arr.concat(1) throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/concat/create-species.js b/test/built-ins/Array/prototype/concat/create-species.js
index 9ca5eb58db..ebf182af92 100644
--- a/test/built-ins/Array/prototype/concat/create-species.js
+++ b/test/built-ins/Array/prototype/concat/create-species.js
@@ -35,8 +35,12 @@ a.constructor[Symbol.species] = Ctor;
 
 result = a.concat();
 
-assert.sameValue(callCount, 1, 'Constructor invoked exactly once');
-assert.sameValue(Object.getPrototypeOf(thisValue), Ctor.prototype);
-assert.sameValue(args.length, 1, 'Constructor invoked with a single argument');
-assert.sameValue(args[0], 0);
-assert.sameValue(result, instance);
+assert.sameValue(callCount, 1, 'The value of callCount is expected to be 1');
+assert.sameValue(
+  Object.getPrototypeOf(thisValue),
+  Ctor.prototype,
+  'Object.getPrototypeOf(this) returns Ctor.prototype'
+);
+assert.sameValue(args.length, 1, 'The value of args.length is expected to be 1');
+assert.sameValue(args[0], 0, 'The value of args[0] is expected to be 0');
+assert.sameValue(result, instance, 'The value of result is expected to equal the value of instance');
diff --git a/test/built-ins/Array/prototype/concat/is-concat-spreadable-get-err.js b/test/built-ins/Array/prototype/concat/is-concat-spreadable-get-err.js
index ab9b4c4be3..7c189f4c04 100644
--- a/test/built-ins/Array/prototype/concat/is-concat-spreadable-get-err.js
+++ b/test/built-ins/Array/prototype/concat/is-concat-spreadable-get-err.js
@@ -35,4 +35,4 @@ Object.defineProperty(o, Symbol.isConcatSpreadable, {
 
 assert.throws(Test262Error, function() {
   Array.prototype.concat.call(o);
-});
+}, 'Array.prototype.concat.call(o) throws a Test262Error exception');
diff --git a/test/built-ins/Array/prototype/concat/is-concat-spreadable-get-order.js b/test/built-ins/Array/prototype/concat/is-concat-spreadable-get-order.js
index 012857565d..18926738ad 100644
--- a/test/built-ins/Array/prototype/concat/is-concat-spreadable-get-order.js
+++ b/test/built-ins/Array/prototype/concat/is-concat-spreadable-get-order.js
@@ -51,8 +51,12 @@ var arr1 = [];
 Object.defineProperty(arr1, "constructor", descConstructor);
 Object.defineProperty(arr1, Symbol.isConcatSpreadable, descSpreadable);
 
-assert.compareArray(arr1.concat(1), [1]);
-assert.compareArray(calls, ["constructor", "isConcatSpreadable"]);
+assert.compareArray(arr1.concat(1), [1], 'arr1.concat(1) must return [1]');
+assert.compareArray(
+  calls,
+  ["constructor", "isConcatSpreadable"],
+  'The value of calls is expected to be ["constructor", "isConcatSpreadable"]'
+);
 
 calls = [];
 
@@ -61,5 +65,9 @@ var arg = {};
 Object.defineProperty(arr2, "constructor", descConstructor);
 Object.defineProperty(arg, Symbol.isConcatSpreadable, descSpreadable);
 
-assert.compareArray(arr2.concat(arg), [arg]);
-assert.compareArray(calls, ["constructor", "isConcatSpreadable"]);
+assert.compareArray(arr2.concat(arg), [arg], 'arr2.concat({}) must return [arg]');
+assert.compareArray(
+  calls,
+  ["constructor", "isConcatSpreadable"],
+  'The value of calls is expected to be ["constructor", "isConcatSpreadable"]'
+);
diff --git a/test/built-ins/Array/prototype/concat/is-concat-spreadable-is-array-proxy-revoked.js b/test/built-ins/Array/prototype/concat/is-concat-spreadable-is-array-proxy-revoked.js
index 126e0e27ed..92cc58f41e 100644
--- a/test/built-ins/Array/prototype/concat/is-concat-spreadable-is-array-proxy-revoked.js
+++ b/test/built-ins/Array/prototype/concat/is-concat-spreadable-is-array-proxy-revoked.js
@@ -47,4 +47,4 @@ var handle = Proxy.revocable(target, {
 
 assert.throws(TypeError, function() {
   [].concat(handle.proxy);
-});
+}, '[].concat(handle.proxy) throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/concat/is-concat-spreadable-proxy-revoked.js b/test/built-ins/Array/prototype/concat/is-concat-spreadable-proxy-revoked.js
index f2ea3a5bd3..74c8eef6ad 100644
--- a/test/built-ins/Array/prototype/concat/is-concat-spreadable-proxy-revoked.js
+++ b/test/built-ins/Array/prototype/concat/is-concat-spreadable-proxy-revoked.js
@@ -40,4 +40,4 @@ handle.revoke();
 
 assert.throws(TypeError, function() {
   [].concat(handle.proxy);
-});
+}, '[].concat(handle.proxy) throws a TypeError exception');
diff --git a/test/built-ins/Array/prototype/concat/is-concat-spreadable-proxy.js b/test/built-ins/Array/prototype/concat/is-concat-spreadable-proxy.js
index f32368c003..c86b5f9dad 100644
--- a/test/built-ins/Array/prototype/concat/is-concat-spreadable-proxy.js
+++ b/test/built-ins/Array/prototype/concat/is-concat-spreadable-proxy.js
@@ -40,12 +40,12 @@ var spreadable = {};
 spreadable[Symbol.isConcatSpreadable] = true;
 var spreadableProxy = new Proxy(spreadable, {});
 
-assert.sameValue([].concat(arrayProxy).length, 0, 'Proxy for an array');
+assert.sameValue([].concat(arrayProxy).length, 0, 'The value of [].concat(arrayProxy).length is expected to be 0');
 assert.sameValue(
-  [].concat(arrayProxyProxy).length, 0, 'Proxy for a proxy for an array'
+  [].concat(arrayProxyProxy).length, 0, 'The value of [].concat(arrayProxyProxy).length is expected to be 0'
 );
 assert.sameValue(
   [].concat(spreadableProxy).length,
   0,
-  'Proxy for an ordinary object with a truthy @@isConcatSpreadable property'
+  'The value of [].concat(spreadableProxy).length is expected to be 0'
 );
diff --git a/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-falsey.js b/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-falsey.js
index 7fa664fbc0..8bd235e2f6 100644
--- a/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-falsey.js
+++ b/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-falsey.js
@@ -36,20 +36,20 @@ var result;
 
 item[Symbol.isConcatSpreadable] = null;
 result = [].concat(item);
-assert.sameValue(result.length, 1);
-assert.sameValue(result[0], item);
+assert.sameValue(result.length, 1, 'The value of result.length is expected to be 1');
+assert.sameValue(result[0], item, 'The value of result[0] is expected to equal the value of item');
 
 item[Symbol.isConcatSpreadable] = false;
 result = [].concat(item);
-assert.sameValue(result.length, 1);
-assert.sameValue(result[0], item);
+assert.sameValue(result.length, 1, 'The value of result.length is expected to be 1');
+assert.sameValue(result[0], item, 'The value of result[0] is expected to equal the value of item');
 
 item[Symbol.isConcatSpreadable] = 0;
 result = [].concat(item);
-assert.sameValue(result.length, 1);
-assert.sameValue(result[0], item);
+assert.sameValue(result.length, 1, 'The value of result.length is expected to be 1');
+assert.sameValue(result[0], item, 'The value of result[0] is expected to equal the value of item');
 
 item[Symbol.isConcatSpreadable] = NaN;
 result = [].concat(item);
-assert.sameValue(result.length, 1);
-assert.sameValue(result[0], item);
+assert.sameValue(result.length, 1, 'The value of result.length is expected to be 1');
+assert.sameValue(result[0], item, 'The value of result[0] is expected to equal the value of item');
diff --git a/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-truthy.js b/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-truthy.js
index c18ab1d012..f7923eb12d 100644
--- a/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-truthy.js
+++ b/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-truthy.js
@@ -34,20 +34,20 @@ var result;
 
 item[Symbol.isConcatSpreadable] = true;
 result = [].concat(item);
-assert.sameValue(result.length, 0);
+assert.sameValue(result.length, 0, 'The value of result.length is expected to be 0');
 
 item[Symbol.isConcatSpreadable] = 86;
 result = [].concat(item);
-assert.sameValue(result.length, 0);
+assert.sameValue(result.length, 0, 'The value of result.length is expected to be 0');
 
 item[Symbol.isConcatSpreadable] = 'string';
 result = [].concat(item);
-assert.sameValue(result.length, 0);
+assert.sameValue(result.length, 0, 'The value of result.length is expected to be 0');
 
 item[Symbol.isConcatSpreadable] = Symbol();
 result = [].concat(item);
-assert.sameValue(result.length, 0);
+assert.sameValue(result.length, 0, 'The value of result.length is expected to be 0');
 
 item[Symbol.isConcatSpreadable] = {};
 result = [].concat(item);
-assert.sameValue(result.length, 0);
+assert.sameValue(result.length, 0, 'The value of result.length is expected to be 0');
diff --git a/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-undefined.js b/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-undefined.js
index 1306800a36..67d277691c 100644
--- a/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-undefined.js
+++ b/test/built-ins/Array/prototype/concat/is-concat-spreadable-val-undefined.js
@@ -38,4 +38,4 @@ var result;
 item[Symbol.isConcatSpreadable] = undefined;
 result = [].concat(item);
 
-assert.sameValue(result.length, 0);
+assert.sameValue(result.length, 0, 'The value of result.length is expected to be 0');
diff --git a/test/built-ins/Array/prototype/concat/length.js b/test/built-ins/Array/prototype/concat/length.js
index 657441f389..92fa5299aa 100644
--- a/test/built-ins/Array/prototype/concat/length.js
+++ b/test/built-ins/Array/prototype/concat/length.js
@@ -25,7 +25,7 @@ info: |
 includes: [propertyHelper.js]
 ---*/
 
-assert.sameValue(Array.prototype.concat.length, 1);
+assert.sameValue(Array.prototype.concat.length, 1, 'The value of Array.prototype.concat.length is expected to be 1');
 
 verifyNotEnumerable(Array.prototype.concat, 'length');
 verifyNotWritable(Array.prototype.concat, 'length');
diff --git a/test/built-ins/Array/prototype/concat/name.js b/test/built-ins/Array/prototype/concat/name.js
index 366b524e5c..90bc748d09 100644
--- a/test/built-ins/Array/prototype/concat/name.js
+++ b/test/built-ins/Array/prototype/concat/name.js
@@ -19,7 +19,11 @@ info: |
 includes: [propertyHelper.js]
 ---*/
 
-assert.sameValue(Array.prototype.concat.name, "concat");
+assert.sameValue(
+  Array.prototype.concat.name,
+  "concat",
+  'The value of Array.prototype.concat.name is expected to be "concat"'
+);
 
 verifyNotEnumerable(Array.prototype.concat, "name");
 verifyNotWritable(Array.prototype.concat, "name");
diff --git a/test/built-ins/Array/prototype/concat/not-a-constructor.js b/test/built-ins/Array/prototype/concat/not-a-constructor.js
index aae4497430..52e60c51bc 100644
--- a/test/built-ins/Array/prototype/concat/not-a-constructor.js
+++ b/test/built-ins/Array/prototype/concat/not-a-constructor.js
@@ -29,5 +29,5 @@ assert.sameValue(
 
 assert.throws(TypeError, () => {
   new Array.prototype.concat([]);
-}, '`new Array.prototype.concat([])` throws TypeError');
+}, 'new Array.prototype.concat([]) throws a TypeError exception');
 
diff --git a/test/built-ins/Array/prototype/concat/prop-desc.js b/test/built-ins/Array/prototype/concat/prop-desc.js
index 897899142e..b086e1589c 100644
--- a/test/built-ins/Array/prototype/concat/prop-desc.js
+++ b/test/built-ins/Array/prototype/concat/prop-desc.js
@@ -14,7 +14,7 @@ info: |
 includes: [propertyHelper.js]
 ---*/
 
-assert.sameValue(typeof Array.prototype.concat, 'function', 'typeof');
+assert.sameValue(typeof Array.prototype.concat, 'function', 'The value of `typeof Array.prototype.concat` is expected to be "function"');
 
 verifyNotEnumerable(Array.prototype, "concat");
 verifyWritable(Array.prototype, "concat");
diff --git a/test/built-ins/Array/prototype/copyWithin/call-with-boolean.js b/test/built-ins/Array/prototype/copyWithin/call-with-boolean.js
index 447f89d7aa..028079e81f 100644
--- a/test/built-ins/Array/prototype/copyWithin/call-with-boolean.js
+++ b/test/built-ins/Array/prototype/copyWithin/call-with-boolean.js
@@ -9,10 +9,10 @@ description: Array.prototype.copyWithin applied to boolean primitive
 assert.sameValue(
   Array.prototype.copyWithin.call(true) instanceof Boolean,
   true,
-  'The result of `(Array.prototype.copyWithin.call(true) instanceof Boolean)` is true'
+  'The result of evaluating (Array.prototype.copyWithin.call(true) instanceof Boolean) is expected to be true'
 );
 assert.sameValue(
   Array.prototype.copyWithin.call(false) instanceof Boolean,
   true,
-  'The result of `(Array.prototype.copyWithin.call(false) instanceof Boolean)` is true'
+  'The result of evaluating (Array.prototype.copyWithin.call(false) instanceof Boolean) is expected to be true'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/coerced-values-end.js b/test/built-ins/Array/prototype/copyWithin/coerced-values-end.js
index ecbd6c021a..166495ea63 100644
--- a/test/built-ins/Array/prototype/copyWithin/coerced-values-end.js
+++ b/test/built-ins/Array/prototype/copyWithin/coerced-values-end.js
@@ -14,44 +14,32 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, 0, null), [0, 1, 2, 3]
-  ),
-  'null value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, 0, null), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(1, 0, null) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, 0, NaN), [0, 1, 2, 3]
-  ),
-  'NaN value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, 0, NaN), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(1, 0, NaN) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, 0, false), [0, 1, 2, 3]
-  ),
-  'false value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, 0, false), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(1, 0, false) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, 0, true), [0, 0, 2, 3]
-  ),
-  'true value coerced to 1'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, 0, true), [0, 0, 2, 3],
+  '[0, 1, 2, 3].copyWithin(1, 0, true) must return [0, 0, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, 0, '-2'), [0, 0, 1, 3]
-  ),
-  'string "-2" value coerced to integer -2'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, 0, '-2'), [0, 0, 1, 3],
+  '[0, 1, 2, 3].copyWithin(1, 0, "-2") must return [0, 0, 1, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, 0, -2.5), [0, 0, 1, 3]
-  ),
-  'float -2.5 value coerced to integer -2'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, 0, -2.5), [0, 0, 1, 3],
+  '[0, 1, 2, 3].copyWithin(1, 0, -2.5) must return [0, 0, 1, 3]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-start.js b/test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-start.js
index 0f0d82c47a..74c7fa35b9 100644
--- a/test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-start.js
+++ b/test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-start.js
@@ -18,16 +18,16 @@ includes: [compareArray.js]
 
 // make a long integer Array
 function longDenseArray(){
-	var a = [0];
-	for(var i = 0; i < 1024; i++){
-		a[i] = i;
-	}
-	return a;
+    var a = [0];
+    for(var i = 0; i < 1024; i++){
+        a[i] = i;
+    }
+    return a;
 }
 
 function shorten(){
-	currArray.length = 20;
-	return 1000;
+    currArray.length = 20;
+    return 1000;
 }
 
 var array = [];
@@ -35,11 +35,9 @@ array.length = 20;
 
 var currArray = longDenseArray();
 
-assert(
-  compareArray(
-    currArray.copyWithin(0, {valueOf: shorten}), array
-  ),
-  'coercion side-effect makes start out of bounds'
+assert.compareArray(
+  currArray.copyWithin(0, {valueOf: shorten}), array,
+  'currArray.copyWithin(0, {valueOf: shorten}) returns array'
 );
 
 currArray = longDenseArray();
@@ -48,12 +46,10 @@ Object.setPrototypeOf(currArray, longDenseArray());
 var array2 = longDenseArray();
 array2.length = 20;
 for(var i = 0; i < 24; i++){
-	array2[i] = Object.getPrototypeOf(currArray)[i+1000];
+    array2[i] = Object.getPrototypeOf(currArray)[i+1000];
 }
 
-assert(
-  compareArray(
-    currArray.copyWithin(0, {valueOf: shorten}), array2
-  ),
-  'coercion side-effect makes start out of bounds with prototype'
+assert.compareArray(
+  currArray.copyWithin(0, {valueOf: shorten}), array2,
+  'currArray.copyWithin(0, {valueOf: shorten}) returns array2'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-target.js b/test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-target.js
index d12f03f462..75c7ab4a79 100644
--- a/test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-target.js
+++ b/test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-target.js
@@ -18,29 +18,27 @@ includes: [compareArray.js]
 
 // make a long integer Array
 function longDenseArray(){
-	var a = [0];
-	for(var i = 0; i < 1024; i++){
-		a[i] = i;
-	}
-	return a;
+    var a = [0];
+    for(var i = 0; i < 1024; i++){
+        a[i] = i;
+    }
+    return a;
 }
 
 function shorten(){
-	currArray.length = 20;
-	return 1;
+    currArray.length = 20;
+    return 1;
 }
 
 var array = longDenseArray();
 array.length = 20;
 for(var i = 0; i < 19; i++){
-	array[i+1000] = array[i+1];
+    array[i+1000] = array[i+1];
 }
 
 var currArray = longDenseArray();
 
-assert(
-  compareArray(
-    currArray.copyWithin(1000, {valueOf: shorten}), array
-  ),
-  'coercion side-effect makes target out of bounds'
+assert.compareArray(
+  currArray.copyWithin(1000, {valueOf: shorten}), array,
+  'currArray.copyWithin(1000, {valueOf: shorten}) returns array'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/coerced-values-start.js b/test/built-ins/Array/prototype/copyWithin/coerced-values-start.js
index 4a3609e0e4..64330e7cf2 100644
--- a/test/built-ins/Array/prototype/copyWithin/coerced-values-start.js
+++ b/test/built-ins/Array/prototype/copyWithin/coerced-values-start.js
@@ -13,60 +13,44 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, undefined), [0, 0, 1, 2]
-  ),
-  'undefined value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, undefined), [0, 0, 1, 2],
+  '[0, 1, 2, 3].copyWithin(1, undefined) must return [0, 0, 1, 2]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, false), [0, 0, 1, 2]
-  ),
-  'false value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, false), [0, 0, 1, 2],
+  '[0, 1, 2, 3].copyWithin(1, false) must return [0, 0, 1, 2]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, NaN), [0, 0, 1, 2]
-  ),
-  'NaN value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, NaN), [0, 0, 1, 2],
+  '[0, 1, 2, 3].copyWithin(1, NaN) must return [0, 0, 1, 2]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, null), [0, 0, 1, 2]
-  ),
-  'null value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, null), [0, 0, 1, 2],
+  '[0, 1, 2, 3].copyWithin(1, null) must return [0, 0, 1, 2]'
 );
 
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, true), [1, 2, 3, 3]
-  ),
-  'true value coerced to 1'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, true), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(0, true) must return [1, 2, 3, 3]'
 );
 
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, '1'), [1, 2, 3, 3]
-  ),
-  'string "1" value coerced to 1'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, '1'), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(0, "1") must return [1, 2, 3, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, 0.5), [0, 0, 1, 2]
-  ),
-  '0.5 float value coerced to integer 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, 0.5), [0, 0, 1, 2],
+  '[0, 1, 2, 3].copyWithin(1, 0.5) must return [0, 0, 1, 2]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, 1.5), [1, 2, 3, 3]
-  ),
-  '1.5 float value coerced to integer 1'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, 1.5), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(0, 1.5) must return [1, 2, 3, 3]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/coerced-values-target.js b/test/built-ins/Array/prototype/copyWithin/coerced-values-target.js
index 9fbf4ecc8a..df6962541e 100644
--- a/test/built-ins/Array/prototype/copyWithin/coerced-values-target.js
+++ b/test/built-ins/Array/prototype/copyWithin/coerced-values-target.js
@@ -13,60 +13,44 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(undefined, 1), [1, 2, 3, 3]
-  ),
-  'undefined value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(undefined, 1), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(undefined, 1) must return [1, 2, 3, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(false, 1), [1, 2, 3, 3]
-  ),
-  'false value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(false, 1), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(false, 1) must return [1, 2, 3, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(NaN, 1), [1, 2, 3, 3]
-  ),
-  'NaN value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(NaN, 1), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(NaN, 1) must return [1, 2, 3, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(null, 1), [1, 2, 3, 3]
-  ),
-  'null value coerced to 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(null, 1), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(null, 1) must return [1, 2, 3, 3]'
 );
 
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(true, 0), [0, 0, 1, 2]
-  ),
-  'true value coerced to 1'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(true, 0), [0, 0, 1, 2],
+  '[0, 1, 2, 3].copyWithin(true, 0) must return [0, 0, 1, 2]'
 );
 
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin('1', 0), [0, 0, 1, 2]
-  ),
-  'string "1" value coerced to 1'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin('1', 0), [0, 0, 1, 2],
+  '[0, 1, 2, 3].copyWithin("1", 0) must return [0, 0, 1, 2]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0.5, 1), [1, 2, 3, 3]
-  ),
-  '0.5 float value coerced to integer 0'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0.5, 1), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(0.5, 1) must return [1, 2, 3, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1.5, 0), [0, 0, 1, 2]
-  ),
-  '1.5 float value coerced to integer 1'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1.5, 0), [0, 0, 1, 2],
+  '[0, 1, 2, 3].copyWithin(1.5, 0) must return [0, 0, 1, 2]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/negative-end.js b/test/built-ins/Array/prototype/copyWithin/negative-end.js
index 22df7e8df5..98de32cd86 100644
--- a/test/built-ins/Array/prototype/copyWithin/negative-end.js
+++ b/test/built-ins/Array/prototype/copyWithin/negative-end.js
@@ -17,58 +17,42 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, 1, -1), [1, 2, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, 1, -1) -> [1, 2, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, 1, -1), [1, 2, 2, 3],
+  '[0, 1, 2, 3].copyWithin(0, 1, -1) must return [1, 2, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(2, 0, -1), [0, 1, 0, 1, 2]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(2, 0, -1) -> [0, 1, 0, 1, 2]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(2, 0, -1), [0, 1, 0, 1, 2],
+  '[0, 1, 2, 3, 4].copyWithin(2, 0, -1) must return [0, 1, 0, 1, 2]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(1, 2, -2), [0, 2, 2, 3, 4]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(1, 2, -2) -> [0, 2, 2, 3, 4]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(1, 2, -2), [0, 2, 2, 3, 4],
+  '[0, 1, 2, 3, 4].copyWithin(1, 2, -2) must return [0, 2, 2, 3, 4]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, -2, -1), [2, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, -2, -1) -> [2, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, -2, -1), [2, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(0, -2, -1) must return [2, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(2, -2, -1), [0, 1, 3, 3, 4]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(2, -2, 1) -> [0, 1, 3, 3, 4]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(2, -2, -1), [0, 1, 3, 3, 4],
+  '[0, 1, 2, 3, 4].copyWithin(2, -2, -1) must return [0, 1, 3, 3, 4]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(-3, -2, -1), [0, 2, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(-3, -2, -1) -> [0, 2, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(-3, -2, -1), [0, 2, 2, 3],
+  '[0, 1, 2, 3].copyWithin(-3, -2, -1) must return [0, 2, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(-2, -3, -1), [0, 1, 2, 2, 3]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(-2, -3, -1) -> [0, 1, 2, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(-2, -3, -1), [0, 1, 2, 2, 3],
+  '[0, 1, 2, 3, 4].copyWithin(-2, -3, -1) must return [0, 1, 2, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(-5, -2, -1), [3, 1, 2, 3, 4]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(-5, -2, -1) -> [3, 1, 2, 3, 4]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(-5, -2, -1), [3, 1, 2, 3, 4],
+  '[0, 1, 2, 3, 4].copyWithin(-5, -2, -1) must return [3, 1, 2, 3, 4]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-end.js b/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-end.js
index 9285d408df..c832f864e3 100644
--- a/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-end.js
+++ b/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-end.js
@@ -17,72 +17,52 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, 1, -10), [0, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, 1, -10) -> [0, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, 1, -10), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(0, 1, -10) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(0, 1, -Infinity), [1, 2, 3, 4, 5]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(0, 1, -Infinity) -> [1, 2, 3, 4, 5]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(0, 1, -Infinity), [1, 2, 3, 4, 5],
+  '[1, 2, 3, 4, 5].copyWithin(0, 1, -Infinity) must return [1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, -2, -10), [0, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, -2, -10) -> [0, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, -2, -10), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(0, -2, -10) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(0, -2, -Infinity), [1, 2, 3, 4, 5]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(0, -2, -Infinity) -> [1, 2, 3, 4, 5]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(0, -2, -Infinity), [1, 2, 3, 4, 5],
+  '[1, 2, 3, 4, 5].copyWithin(0, -2, -Infinity) must return [1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, -9, -10), [0, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, -9, -10) -> [0, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, -9, -10), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(0, -9, -10) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(0, -9, -Infinity), [1, 2, 3, 4, 5]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(0, -9, -Infinity) -> [1, 2, 3, 4, 5]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(0, -9, -Infinity), [1, 2, 3, 4, 5],
+  '[1, 2, 3, 4, 5].copyWithin(0, -9, -Infinity) must return [1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(-3, -2, -10), [0, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(-3, -2, -10) -> [0, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(-3, -2, -10), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(-3, -2, -10) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(-3, -2, -Infinity), [1, 2, 3, 4, 5]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(-3, -2, -Infinity) -> [1, 2, 3, 4, 5]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(-3, -2, -Infinity), [1, 2, 3, 4, 5],
+  '[1, 2, 3, 4, 5].copyWithin(-3, -2, -Infinity) must return [1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(-7, -8, -9), [0, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(-7, -8, -9) -> [0, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(-7, -8, -9), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(-7, -8, -9) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(-7, -8, -Infinity), [1, 2, 3, 4, 5]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(-7, -8, -Infinity) -> [1, 2, 3, 4, 5]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(-7, -8, -Infinity), [1, 2, 3, 4, 5],
+  '[1, 2, 3, 4, 5].copyWithin(-7, -8, -Infinity) must return [1, 2, 3, 4, 5]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-start.js b/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-start.js
index a5dd431a4f..4afbbcc402 100644
--- a/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-start.js
+++ b/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-start.js
@@ -14,60 +14,44 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, -10), [0, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, -10) -> [0, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, -10), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(0, -10) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(0, -Infinity), [1, 2, 3, 4, 5]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(0, -Infinity) -> [1, 2, 3, 4, 5]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(0, -Infinity), [1, 2, 3, 4, 5],
+  '[1, 2, 3, 4, 5].copyWithin(0, -Infinity) must return [1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(2, -10), [0, 1, 0, 1, 2]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(2, -2) -> [0, 1, 0, 1, 2]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(2, -10), [0, 1, 0, 1, 2],
+  '[0, 1, 2, 3, 4].copyWithin(2, -10) must return [0, 1, 0, 1, 2]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(2, -Infinity), [1, 2, 1, 2, 3]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(2, -Infinity) -> [1, 2, 1, 2, 3]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(2, -Infinity), [1, 2, 1, 2, 3],
+  '[1, 2, 3, 4, 5].copyWithin(2, -Infinity) must return [1, 2, 1, 2, 3]'
 );
 
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(10, -10), [0, 1, 2, 3, 4]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(10, -10) -> [0, 1, 2, 3, 4]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(10, -10), [0, 1, 2, 3, 4],
+  '[0, 1, 2, 3, 4].copyWithin(10, -10) must return [0, 1, 2, 3, 4]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(10, -Infinity), [1, 2, 3, 4, 5]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(10, -Infinity) -> [1, 2, 3, 4, 5]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(10, -Infinity), [1, 2, 3, 4, 5],
+  '[1, 2, 3, 4, 5].copyWithin(10, -Infinity) must return [1, 2, 3, 4, 5]'
 );
 
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(-9, -10), [0, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(-9, -10) -> [0, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(-9, -10), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(-9, -10) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(-9, -Infinity), [1, 2, 3, 4, 5]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(-9, -Infinity) -> [1, 2, 3, 4, 5]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(-9, -Infinity), [1, 2, 3, 4, 5],
+  '[1, 2, 3, 4, 5].copyWithin(-9, -Infinity) must return [1, 2, 3, 4, 5]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-target.js b/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-target.js
index e78c2a6d18..021f196f58 100644
--- a/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-target.js
+++ b/test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-target.js
@@ -14,30 +14,22 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(-10, 0), [0, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(-10, 0) -> [0, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(-10, 0), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(-10, 0) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(-Infinity, 0), [1, 2, 3, 4, 5]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(-Infinity, 0) -> [1, 2, 3, 4, 5]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(-Infinity, 0), [1, 2, 3, 4, 5],
+  '[1, 2, 3, 4, 5].copyWithin(-Infinity, 0) must return [1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(-10, 2), [2, 3, 4, 3, 4]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(-10, 2) -> [2, 3, 4, 3, 4]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(-10, 2), [2, 3, 4, 3, 4],
+  '[0, 1, 2, 3, 4].copyWithin(-10, 2) must return [2, 3, 4, 3, 4]'
 );
 
-assert(
-  compareArray(
-    [1, 2, 3, 4, 5].copyWithin(-Infinity, 2), [3, 4, 5, 4, 5]
-  ),
-  '[1, 2, 3, 4, 5].copyWithin(-Infinity, 2) -> [3, 4, 5, 4, 5]'
+assert.compareArray(
+  [1, 2, 3, 4, 5].copyWithin(-Infinity, 2), [3, 4, 5, 4, 5],
+  '[1, 2, 3, 4, 5].copyWithin(-Infinity, 2) must return [3, 4, 5, 4, 5]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/negative-start.js b/test/built-ins/Array/prototype/copyWithin/negative-start.js
index cda222a507..8f3d862e3d 100644
--- a/test/built-ins/Array/prototype/copyWithin/negative-start.js
+++ b/test/built-ins/Array/prototype/copyWithin/negative-start.js
@@ -14,44 +14,32 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, -1), [3, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, -1) -> [3, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, -1), [3, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(0, -1) must return [3, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(2, -2), [0, 1, 3, 4, 4]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(2, -2) -> [0, 1, 3, 4, 4]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(2, -2), [0, 1, 3, 4, 4],
+  '[0, 1, 2, 3, 4].copyWithin(2, -2) must return [0, 1, 3, 4, 4]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(1, -2), [0, 3, 4, 3, 4]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(1, -2) -> [0, 3, 4, 3, 4]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(1, -2), [0, 3, 4, 3, 4],
+  '[0, 1, 2, 3, 4].copyWithin(1, -2) must return [0, 3, 4, 3, 4]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(-1, -2), [0, 1, 2, 2]
-  ),
-  '[0, 1, 2, 3].copyWithin(-1, -2) -> [ 0, 1, 2, 2 ]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(-1, -2), [0, 1, 2, 2],
+  '[0, 1, 2, 3].copyWithin(-1, -2) must return [0, 1, 2, 2]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(-2, -3), [0, 1, 2, 2, 3]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(-2, -3) -> [0, 1, 2, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(-2, -3), [0, 1, 2, 2, 3],
+  '[0, 1, 2, 3, 4].copyWithin(-2, -3) must return [0, 1, 2, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(-5, -2), [3, 4, 2, 3, 4]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(-5, -2) -> [3, 4, 2, 3, 4]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(-5, -2), [3, 4, 2, 3, 4],
+  '[0, 1, 2, 3, 4].copyWithin(-5, -2) must return [3, 4, 2, 3, 4]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/negative-target.js b/test/built-ins/Array/prototype/copyWithin/negative-target.js
index b1a4ebd463..5ae4a18f03 100644
--- a/test/built-ins/Array/prototype/copyWithin/negative-target.js
+++ b/test/built-ins/Array/prototype/copyWithin/negative-target.js
@@ -14,23 +14,17 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(-1, 0), [0, 1, 2, 0]
-  ),
-  '[0, 1, 2, 3].copyWithin(-1, 0) -> [0, 1, 2, 0]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(-1, 0), [0, 1, 2, 0],
+  '[0, 1, 2, 3].copyWithin(-1, 0) must return [0, 1, 2, 0]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4].copyWithin(-2, 2), [0, 1, 2, 2, 3]
-  ),
-  '[0, 1, 2, 3, 4].copyWithin(-2, 2) -> [0, 1, 2, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3, 4].copyWithin(-2, 2), [0, 1, 2, 2, 3],
+  '[0, 1, 2, 3, 4].copyWithin(-2, 2) must return [0, 1, 2, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(-1, 2), [0, 1, 2, 2]
-  ),
-  '[0, 1, 2, 3].copyWithin(-1, 2) -> [0, 1, 2, 2]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(-1, 2), [0, 1, 2, 2],
+  '[0, 1, 2, 3].copyWithin(-1, 2) must return [0, 1, 2, 2]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-end.js b/test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-end.js
index ebea5270dd..ae13ec2dd6 100644
--- a/test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-end.js
+++ b/test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-end.js
@@ -33,30 +33,22 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, 1, 6), [1, 2, 3, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, 1, 6) -> [1, 2, 3, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, 1, 6), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(0, 1, 6) must return [1, 2, 3, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, 1, Infinity), [1, 2, 3, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, 1, Infinity) -> [1, 2, 3, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, 1, Infinity), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(0, 1, Infinity) must return [1, 2, 3, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(1, 3, 6), [0, 3, 4, 5, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(1, 3, 6) -> [0, 3, 4, 5, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(1, 3, 6), [0, 3, 4, 5, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(1, 3, 6) must return [0, 3, 4, 5, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(1, 3, Infinity), [0, 3, 4, 5, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(1, 3, Infinity) -> [0, 3, 4, 5, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(1, 3, Infinity), [0, 3, 4, 5, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(1, 3, Infinity) must return [0, 3, 4, 5, 4, 5]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-target-and-start.js b/test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-target-and-start.js
index cc75551e9b..5230f1d8cb 100644
--- a/test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-target-and-start.js
+++ b/test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-target-and-start.js
@@ -27,109 +27,79 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(6, 0), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(6, 0) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(6, 0), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(6, 0) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(7, 0), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(6, 0) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(7, 0), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(7, 0) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(Infinity, 0), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(Infinity, 0) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(Infinity, 0), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(Infinity, 0) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(6, 2), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(6, 2) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(6, 2), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(6, 2) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(7, 2), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(7, 2) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(7, 2), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(7, 2) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(Infinity, 2), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(Infinity, 2) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(Infinity, 2), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(Infinity, 2) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(0, 6), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(0, 6) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(0, 6), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(0, 6) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(0, 7), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(0, 7) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(0, 7), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(0, 7) must return [0, 1, 2, 3, 4, 5]'
 );
 
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(0, Infinity), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(0, Infinity) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(0, Infinity), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(0, Infinity) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(2, 6), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(2, 6) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(2, 6), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(2, 6) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(1, 7), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(1, 7) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(1, 7), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(1, 7) must return [0, 1, 2, 3, 4, 5]'
 );
 
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(3, Infinity), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(3, Infinity) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(3, Infinity), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(3, Infinity) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(6, 6), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(6, 6) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(6, 6), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(6, 6) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(10, 10), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(10, 10) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(10, 10), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(10, 10) must return [0, 1, 2, 3, 4, 5]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(Infinity, Infinity), [0, 1, 2, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(Infinity, Infinity) => [0, 1, 2, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(Infinity, Infinity), [0, 1, 2, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(Infinity, Infinity) must return [0, 1, 2, 3, 4, 5]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/non-negative-target-and-start.js b/test/built-ins/Array/prototype/copyWithin/non-negative-target-and-start.js
index d1840a720f..cf8f60912f 100644
--- a/test/built-ins/Array/prototype/copyWithin/non-negative-target-and-start.js
+++ b/test/built-ins/Array/prototype/copyWithin/non-negative-target-and-start.js
@@ -31,26 +31,18 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    ['a', 'b', 'c', 'd', 'e', 'f'].copyWithin(0, 0), ['a', 'b', 'c', 'd', 'e', 'f']
-  )
-);
+assert(compareArray(
+  ['a', 'b', 'c', 'd', 'e', 'f'].copyWithin(0, 0), ['a', 'b', 'c', 'd', 'e', 'f']
+), 'compareArray( ["a", "b", "c", "d", "e", "f"].copyWithin(0, 0), ["a", "b", "c", "d", "e", "f"] ) must return true');
 
-assert(
-  compareArray(
-    ['a', 'b', 'c', 'd', 'e', 'f'].copyWithin(0, 2), ['c', 'd', 'e', 'f', 'e', 'f']
-  )
-);
+assert(compareArray(
+  ['a', 'b', 'c', 'd', 'e', 'f'].copyWithin(0, 2), ['c', 'd', 'e', 'f', 'e', 'f']
+), 'compareArray( ["a", "b", "c", "d", "e", "f"].copyWithin(0, 2), ["c", "d", "e", "f", "e", "f"] ) must return true');
 
-assert(
-  compareArray(
-    ['a', 'b', 'c', 'd', 'e', 'f'].copyWithin(3, 0), ['a', 'b', 'c', 'a', 'b', 'c']
-  )
-);
+assert(compareArray(
+  ['a', 'b', 'c', 'd', 'e', 'f'].copyWithin(3, 0), ['a', 'b', 'c', 'a', 'b', 'c']
+), 'compareArray( ["a", "b", "c", "d", "e", "f"].copyWithin(3, 0), ["a", "b", "c", "a", "b", "c"] ) must return true');
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(1, 4), [0, 4, 5, 3, 4, 5]
-  )
-);
+assert(compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(1, 4), [0, 4, 5, 3, 4, 5]
+), 'compareArray( [0, 1, 2, 3, 4, 5].copyWithin(1, 4), [0, 4, 5, 3, 4, 5] ) must return true');
diff --git a/test/built-ins/Array/prototype/copyWithin/non-negative-target-start-and-end.js b/test/built-ins/Array/prototype/copyWithin/non-negative-target-start-and-end.js
index a3c02b63d2..2d1d6aa93c 100644
--- a/test/built-ins/Array/prototype/copyWithin/non-negative-target-start-and-end.js
+++ b/test/built-ins/Array/prototype/copyWithin/non-negative-target-start-and-end.js
@@ -33,25 +33,19 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, 0, 0), [0, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, 0, 0) -> [0, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, 0, 0), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(0, 0, 0) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, 0, 2), [0, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, 0, 2) -> [0, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, 0, 2), [0, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(0, 0, 2) must return [0, 1, 2, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, 1, 2), [1, 1, 2, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, 1, 2) -> [1, 1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, 1, 2), [1, 1, 2, 3],
+  '[0, 1, 2, 3].copyWithin(0, 1, 2) must return [1, 1, 2, 3]'
 );
 
 /*
@@ -65,16 +59,12 @@ assert(
  *  from = 0 + 2 - 1
  *  to = 1 + 2 - 1
  */
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(1, 0, 2), [0, 0, 1, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(1, 0, 2) -> [0, 0, 1, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(1, 0, 2), [0, 0, 1, 3],
+  '[0, 1, 2, 3].copyWithin(1, 0, 2) must return [0, 0, 1, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3, 4, 5].copyWithin(1, 3, 5), [0, 3, 4, 3, 4, 5]
-  ),
-  '[0, 1, 2, 3, 4, 5].copyWithin(1, 3, 5) -> [0, 3, 4, 3, 4, 5]'
+assert.compareArray(
+  [0, 1, 2, 3, 4, 5].copyWithin(1, 3, 5), [0, 3, 4, 3, 4, 5],
+  '[0, 1, 2, 3, 4, 5].copyWithin(1, 3, 5) must return [0, 3, 4, 3, 4, 5]'
 );
diff --git a/test/built-ins/Array/prototype/copyWithin/undefined-end.js b/test/built-ins/Array/prototype/copyWithin/undefined-end.js
index e81642c36e..a0de264e5c 100644
--- a/test/built-ins/Array/prototype/copyWithin/undefined-end.js
+++ b/test/built-ins/Array/prototype/copyWithin/undefined-end.js
@@ -14,16 +14,12 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, 1, undefined), [1, 2, 3, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, 1, undefined) -> [1, 2, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, 1, undefined), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(0, 1, undefined) must return [1, 2, 3, 3]'
 );
 
-assert(
-  compareArray(
-    [0, 1, 2, 3].copyWithin(0, 1), [1, 2, 3, 3]
-  ),
-  '[0, 1, 2, 3].copyWithin(0, 1) -> [1, 2, 3, 3]'
+assert.compareArray(
+  [0, 1, 2, 3].copyWithin(0, 1), [1, 2, 3, 3],
+  '[0, 1, 2, 3].copyWithin(0, 1) must return [1, 2, 3, 3]'
 );
diff --git a/test/built-ins/Array/prototype/fill/coerced-indexes.js b/test/built-ins/Array/prototype/fill/coerced-indexes.js
index 0b064cf5d4..f5a4707c0e 100644
--- a/test/built-ins/Array/prototype/fill/coerced-indexes.js
+++ b/test/built-ins/Array/prototype/fill/coerced-indexes.js
@@ -18,72 +18,58 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray([0, 0].fill(1, undefined), [1, 1]),
-  '`undefined` start coerced to 0'
+assert.compareArray([0, 0].fill(1, undefined), [1, 1],
+  '[0, 0].fill(1, undefined) must return [1, 1]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, 0, undefined), [1, 1]),
-  'If end is undefined, let relativeEnd be len'
+assert.compareArray([0, 0].fill(1, 0, undefined), [1, 1],
+  '[0, 0].fill(1, 0, undefined) must return [1, 1]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, null), [1, 1]),
-  '`null` start coerced to 0'
+assert.compareArray([0, 0].fill(1, null), [1, 1],
+  '[0, 0].fill(1, null) must return [1, 1]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, 0, null), [0, 0]),
-  '`null` end coerced to 0'
+assert.compareArray([0, 0].fill(1, 0, null), [0, 0],
+  '[0, 0].fill(1, 0, null) must return [0, 0]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, true), [0, 1]),
-  '`true` start coerced to 1'
+assert.compareArray([0, 0].fill(1, true), [0, 1],
+  '[0, 0].fill(1, true) must return [0, 1]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, 0, true), [1, 0]),
-  '`true` end coerced to 1'
+assert.compareArray([0, 0].fill(1, 0, true), [1, 0],
+  '[0, 0].fill(1, 0, true) must return [1, 0]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, false), [1, 1]),
-  '`false` start coerced to 0'
+assert.compareArray([0, 0].fill(1, false), [1, 1],
+  '[0, 0].fill(1, false) must return [1, 1]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, 0, false), [0, 0]),
-  '`false` end coerced to 0'
+assert.compareArray([0, 0].fill(1, 0, false), [0, 0],
+  '[0, 0].fill(1, 0, false) must return [0, 0]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, NaN), [1, 1]),
-  '`NaN` start coerced to 0'
+assert.compareArray([0, 0].fill(1, NaN), [1, 1],
+  '[0, 0].fill(1, NaN) must return [1, 1]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, 0, NaN), [0, 0]),
-  '`NaN` end coerced to 0'
+assert.compareArray([0, 0].fill(1, 0, NaN), [0, 0],
+  '[0, 0].fill(1, 0, NaN) must return [0, 0]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, '1'), [0, 1]),
-  'string start coerced'
+assert.compareArray([0, 0].fill(1, '1'), [0, 1],
+  '[0, 0].fill(1, "1") must return [0, 1]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, 0, '1'), [1, 0]),
-  'string end coerced'
+assert.compareArray([0, 0].fill(1, 0, '1'), [1, 0],
+  '[0, 0].fill(1, 0, "1") must return [1, 0]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, 1.5), [0, 1]),
-  'start as a float number coerced'
+assert.compareArray([0, 0].fill(1, 1.5), [0, 1],
+  '[0, 0].fill(1, 1.5) must return [0, 1]'
 );
 
-assert(
-  compareArray([0, 0].fill(1, 0, 1.5), [1, 0]),
-  'end as a float number coerced'
+assert.compareArray([0, 0].fill(1, 0, 1.5), [1, 0],
+  '[0, 0].fill(1, 0, 1.5) must return [1, 0]'
 );
diff --git a/test/built-ins/Array/prototype/fill/fill-values-custom-start-and-end.js b/test/built-ins/Array/prototype/fill/fill-values-custom-start-and-end.js
index ef23dc53ec..cc92a23ea5 100644
--- a/test/built-ins/Array/prototype/fill/fill-values-custom-start-and-end.js
+++ b/test/built-ins/Array/prototype/fill/fill-values-custom-start-and-end.js
@@ -19,8 +19,20 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(compareArray([0, 0, 0].fill(8, 1, 2), [0, 8, 0]));
-assert(compareArray([0, 0, 0, 0, 0].fill(8, -3, 4), [0, 0, 8, 8, 0]));
-assert(compareArray([0, 0, 0, 0, 0].fill(8, -2, -1), [0, 0, 0, 8, 0]));
-assert(compareArray([0, 0, 0, 0, 0].fill(8, -1, -3), [0, 0, 0, 0, 0]));
-assert(compareArray([, , , , 0].fill(8, 1, 3), [, 8, 8, , 0]));
+assert.compareArray([0, 0, 0].fill(8, 1, 2), [0, 8, 0], '[0, 0, 0].fill(8, 1, 2) must return [0, 8, 0]');
+assert.compareArray(
+  [0, 0, 0, 0, 0].fill(8, -3, 4),
+  [0, 0, 8, 8, 0],
+  '[0, 0, 0, 0, 0].fill(8, -3, 4) must return [0, 0, 8, 8, 0]'
+);
+assert.compareArray(
+  [0, 0, 0, 0, 0].fill(8, -2, -1),
+  [0, 0, 0, 8, 0],
+  '[0, 0, 0, 0, 0].fill(8, -2, -1) must return [0, 0, 0, 8, 0]'
+);
+assert.compareArray(
+  [0, 0, 0, 0, 0].fill(8, -1, -3),
+  [0, 0, 0, 0, 0],
+  '[0, 0, 0, 0, 0].fill(8, -1, -3) must return [0, 0, 0, 0, 0]'
+);
+assert.compareArray([, , , , 0].fill(8, 1, 3), [, 8, 8, , 0], '[, , , , 0].fill(8, 1, 3) must return [, 8, 8, , 0]');
diff --git a/test/built-ins/Array/prototype/fill/fill-values-relative-end.js b/test/built-ins/Array/prototype/fill/fill-values-relative-end.js
index 67131c43f7..bd6e696d26 100644
--- a/test/built-ins/Array/prototype/fill/fill-values-relative-end.js
+++ b/test/built-ins/Array/prototype/fill/fill-values-relative-end.js
@@ -17,17 +17,14 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray([0, 0, 0].fill(8, 0, 1), [8, 0, 0]),
-  'Fill elements from custom end position'
+assert.compareArray([0, 0, 0].fill(8, 0, 1), [8, 0, 0],
+  '[0, 0, 0].fill(8, 0, 1) must return [8, 0, 0]'
 );
 
-assert(
-  compareArray([0, 0, 0].fill(8, 0, -1), [8, 8, 0]),
-  'negative end sets final position to max((this.length + relativeEnd), 0)'
+assert.compareArray([0, 0, 0].fill(8, 0, -1), [8, 8, 0],
+  '[0, 0, 0].fill(8, 0, -1) must return [8, 8, 0]'
 );
 
-assert(
-  compareArray([0, 0, 0].fill(8, 0, 5), [8, 8, 8]),
-  'end position is never higher than of this.length'
+assert.compareArray([0, 0, 0].fill(8, 0, 5), [8, 8, 8],
+  '[0, 0, 0].fill(8, 0, 5) must return [8, 8, 8]'
 );
diff --git a/test/built-ins/Array/prototype/fill/fill-values-relative-start.js b/test/built-ins/Array/prototype/fill/fill-values-relative-start.js
index 9be8548c4b..a79ea7447b 100644
--- a/test/built-ins/Array/prototype/fill/fill-values-relative-start.js
+++ b/test/built-ins/Array/prototype/fill/fill-values-relative-start.js
@@ -14,17 +14,14 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(
-  compareArray([0, 0, 0].fill(8, 1), [0, 8, 8]),
-  'Fill elements from custom start position'
+assert.compareArray([0, 0, 0].fill(8, 1), [0, 8, 8],
+  '[0, 0, 0].fill(8, 1) must return [0, 8, 8]'
 );
 
-assert(
-  compareArray([0, 0, 0].fill(8, 4), [0, 0, 0]),
-  'start position is never higher than this.length'
+assert.compareArray([0, 0, 0].fill(8, 4), [0, 0, 0],
+  '[0, 0, 0].fill(8, 4) must return [0, 0, 0]'
 );
 
-assert(
-  compareArray([0, 0, 0].fill(8, -1), [0, 0, 8]),
-  'negative start sets initial position to max((this.length + relativeStart),0)'
+assert.compareArray([0, 0, 0].fill(8, -1), [0, 0, 8],
+  '[0, 0, 0].fill(8, -1) must return [0, 0, 8]'
 );
diff --git a/test/built-ins/Array/prototype/fill/fill-values.js b/test/built-ins/Array/prototype/fill/fill-values.js
index f1b08dd88b..595544e8bc 100644
--- a/test/built-ins/Array/prototype/fill/fill-values.js
+++ b/test/built-ins/Array/prototype/fill/fill-values.js
@@ -24,13 +24,10 @@ info: |
 includes: [compareArray.js]
 ---*/
 
-assert(compareArray([].fill(8), []));
+assert.compareArray([].fill(8), [], '[].fill(8) must return []');
 
-assert(compareArray(
-  [0, 0].fill(), [undefined, undefined]
-));
+assert.compareArray([0, 0].fill(), [undefined, undefined], '[0, 0].fill() must return [undefined, undefined]');
 
-assert(
-  compareArray([0, 0, 0].fill(8), [8, 8, 8]),
-  'Default start and end indexes are 0 and this.length'
+assert.compareArray([0, 0, 0].fill(8), [8, 8, 8],
+  '[0, 0, 0].fill(8) must return [8, 8, 8]'
 );
diff --git a/test/built-ins/Array/prototype/flat/array-like-objects.js b/test/built-ins/Array/prototype/flat/array-like-objects.js
index 9c9303ff1a..5699b11c17 100644
--- a/test/built-ins/Array/prototype/flat/array-like-objects.js
+++ b/test/built-ins/Array/prototype/flat/array-like-objects.js
@@ -14,18 +14,18 @@ function getArgumentsObject() {
 
 var a = getArgumentsObject([1], [2]);
 var actual = [].flat.call(a);
-assert.compareArray(actual, [1, 2], 'arguments objects');
+assert.compareArray(actual, [1, 2], 'The value of actual is expected to be [1, 2]');
 
 a = {
   length: 1,
   0: [1],
 };
 actual = [].flat.call(a);
-assert.compareArray(actual, [1], 'array-like objects');
+assert.compareArray(actual, [1], 'The value of actual is expected to be [1]');
 
 a = {
   length: undefined,
   0: [1],
 };
 actual = [].flat.call(a);
-assert.compareArray(actual, [], 'array-like objects; undefined length');
+assert.compareArray(actual, [], 'The value of actual is expected to be []');
diff --git a/test/built-ins/Array/prototype/flat/bound-function-call.js b/test/built-ins/Array/prototype/flat/bound-function-call.js
index efff7d963c..40d93a6aac 100644
--- a/test/built-ins/Array/prototype/flat/bound-function-call.js
+++ b/test/built-ins/Array/prototype/flat/bound-function-call.js
@@ -14,4 +14,4 @@ var a = [
 ];
 var actual = [].flat.bind(a)();
 
-assert.compareArray(actual, [0, 1], 'bound flat');
+assert.compareArray(actual, [0, 1], 'The value of actual is expected to be [0, 1]');
diff --git a/test/built-ins/Array/prototype/flat/empty-array-elements.js b/test/built-ins/Array/prototype/flat/empty-array-elements.js
index c78eb3c660..3d8d8b1b3f 100644
--- a/test/built-ins/Array/prototype/flat/empty-array-elements.js
+++ b/test/built-ins/Array/prototype/flat/empty-array-elements.js
@@ -9,16 +9,16 @@ features: [Array.prototype.flat]
 ---*/
 
 var a = {};
-assert.compareArray([].flat(), []);
+assert.compareArray([].flat(), [], '[].flat() must return []');
 assert.compareArray([
   [],
   []
-].flat(), []);
+].flat(), [], '[ [], [] ].flat() must return []');
 assert.compareArray([
   [],
   [1]
-].flat(), [1]);
+].flat(), [1], '[ [], [1] ].flat() must return [1]');
 assert.compareArray([
   [],
   [1, a]
-].flat(), [1, a]);
+].flat(), [1, a], '[ [], [1, a] ].flat() must return [1, a]');
diff --git a/test/built-ins/Array/prototype/flat/empty-object-elements.js b/test/built-ins/Array/prototype/flat/empty-object-elements.js
index dc3e92eb4f..34e339843f 100644
--- a/test/built-ins/Array/prototype/flat/empty-object-elements.js
+++ b/test/built-ins/Array/prototype/flat/empty-object-elements.js
@@ -11,12 +11,12 @@ features: [Array.prototype.flat]
 var a = {},
   b = {};
 
-assert.compareArray([a].flat(), [a]);
-assert.compareArray([a, [b]].flat(), [a, b]);
+assert.compareArray([a].flat(), [a], '[a].flat() must return [a]');
+assert.compareArray([a, [b]].flat(), [a, b], '[a, [b]].flat() must return [a, b]');
 assert.compareArray([
   [a], b
-].flat(), [a, b]);
+].flat(), [a, b], '[ [a], b ].flat() must return [a, b]');
 assert.compareArray([
   [a],
   [b]
-].flat(), [a, b]);
+].flat(), [a, b], '[ [a], [b] ].flat() must return [a, b]');
diff --git a/test/built-ins/Array/prototype/flat/non-numeric-depth-should-not-throw.js b/test/built-ins/Array/prototype/flat/non-numeric-depth-should-not-throw.js
index 946465094c..94c1ca65fd 100644
--- a/test/built-ins/Array/prototype/flat/non-numeric-depth-should-not-throw.js
+++ b/test/built-ins/Array/prototype/flat/non-numeric-depth-should-not-throw.js
@@ -14,30 +14,30 @@ var expected = a;
 // non integral string depthNum is converted to 0
 var depthNum = 'TestString';
 var actual = a.flat(depthNum);
-assert(compareArray(actual, expected), 'non integral string depthNum');
+assert.compareArray(actual, expected, 'The value of actual is expected to equal the value of expected');
 
 // object type depthNum is converted to 0
 depthNum = {};
 actual = a.flat(depthNum);
-assert(compareArray(actual, expected), 'object type depthNum');
+assert.compareArray(actual, expected, 'The value of actual is expected to equal the value of expected');
 
 // negative infinity depthNum is converted to 0
 depthNum = Number.NEGATIVE_INFINITY;
 actual = a.flat(depthNum);
-assert(compareArray(actual, expected), 'negative infinity depthNum');
+assert.compareArray(actual, expected, 'The value of actual is expected to equal the value of expected');
 
 // positive zero depthNum is converted to 0
 depthNum = +0;
 actual = a.flat(depthNum);
-assert(compareArray(actual, expected), 'positive zero depthNum');
+assert.compareArray(actual, expected, 'The value of actual is expected to equal the value of expected');
 
 // negative zero depthNum is converted to 0
 depthNum = -0;
 actual = a.flat(depthNum);
-assert(compareArray(actual, expected), 'negative zero depthNum');
+assert.compareArray(actual, expected, 'The value of actual is expected to equal the value of expected');
 
 // integral string depthNum is converted to an integer
 depthNum = '1';
 actual = a.flat(depthNum);
 expected = [1, 2]
-assert(compareArray(actual, expected), 'integral string depthNum');
+assert.compareArray(actual, expected, 'The value of actual is expected to equal the value of expected');
diff --git a/test/built-ins/Array/prototype/flat/null-undefined-elements.js b/test/built-ins/Array/prototype/flat/null-undefined-elements.js
index a252f10bc8..e65c7b33b2 100644
--- a/test/built-ins/Array/prototype/flat/null-undefined-elements.js
+++ b/test/built-ins/Array/prototype/flat/null-undefined-elements.js
@@ -10,11 +10,23 @@ features: [Array.prototype.flat]
 
 var a = [void 0];
 
-assert(compareArray([1, null, void 0].flat(), [1, null, undefined]));
-assert(compareArray([1, [null, void 0]].flat(), [1, null, undefined]));
-assert(compareArray([
+assert.compareArray(
+  [1, null, void 0].flat(),
+  [1, null, undefined],
+  '[1, null, void 0].flat() must return [1, null, undefined]'
+);
+assert.compareArray(
+  [1, [null, void 0]].flat(),
+  [1, null, undefined],
+  '[1, [null, void 0]].flat() must return [1, null, undefined]'
+);
+assert.compareArray([
   [null, void 0],
   [null, void 0]
-].flat(), [null, undefined, null, undefined]));
-assert(compareArray([1, [null, a]].flat(1), [1, null, a]));
-assert(compareArray([1, [null, a]].flat(2), [1, null, undefined]));
+].flat(), [null, undefined, null, undefined], '[ [null, void 0], [null, void 0] ].flat() must return [null, undefined, null, undefined]');
+assert.compareArray([1, [null, a]].flat(1), [1, null, a], '[1, [null, a]].flat(1) must return [1, null, a]');
+assert.compareArray(
+  [1, [null, a]].flat(2),
+  [1, null, undefined],
+  '[1, [null, a]].flat(2) must return [1, null, undefined]'
+);
diff --git a/test/built-ins/Array/prototype/flat/positive-infinity.js b/test/built-ins/Array/prototype/flat/positive-infinity.js
index 381200976a..04b5f28e7b 100644
--- a/test/built-ins/Array/prototype/flat/positive-infinity.js
+++ b/test/built-ins/Array/prototype/flat/positive-infinity.js
@@ -9,4 +9,4 @@ features: [Array.prototype.flat]
 ---*/
 
 var a = [1, [2, [3, [4]]]]
-assert(compareArray(a.flat(Number.POSITIVE_INFINITY), [1, 2, 3, 4]), 'positive infinity depthNum');
+assert.compareArray(a.flat(Number.POSITIVE_INFINITY), [1, 2, 3, 4], 'a.flat(Number.POSITIVE_INFINITY) must return [1, 2, 3, 4]');
diff --git a/test/built-ins/Array/prototype/flat/proxy-access-count.js b/test/built-ins/Array/prototype/flat/proxy-access-count.js
index 9dbc4839c2..c6c27e25c6 100644
--- a/test/built-ins/Array/prototype/flat/proxy-access-count.js
+++ b/test/built-ins/Array/prototype/flat/proxy-access-count.js
@@ -32,5 +32,5 @@ const tier1 = new Proxy([2, [3, [4, 2], 2], 5, tier2, 6], handler);
 
 Array.prototype.flat.call(tier1, 3);
 
-assert.compareArray(getCalls, ["length", "constructor", "0", "1", "2", "3", "length", "0", "1", "4"], 'getProperty by .flat should occur exactly once per property and once for length and constructor');
-assert.compareArray(hasCalls, ["0", "1", "2", "3", "0", "1", "4"], 'hasProperty by .flat should occur exactly once per property');
+assert.compareArray(getCalls, ["length", "constructor", "0", "1", "2", "3", "length", "0", "1", "4"], 'The value of getCalls is expected to be ["length", "constructor", "0", "1", "2", "3", "length", "0", "1", "4"]');
+assert.compareArray(hasCalls, ["0", "1", "2", "3", "0", "1", "4"], 'The value of hasCalls is expected to be ["0", "1", "2", "3", "0", "1", "4"]');
diff --git a/test/built-ins/Array/prototype/flatMap/array-like-objects-nested.js b/test/built-ins/Array/prototype/flatMap/array-like-objects-nested.js
index 82f5a2dc4a..af36d4d232 100644
--- a/test/built-ins/Array/prototype/flatMap/array-like-objects-nested.js
+++ b/test/built-ins/Array/prototype/flatMap/array-like-objects-nested.js
@@ -50,8 +50,8 @@ var obj3 = {
 
 var arr = [obj1, obj2, obj3];
 var actual = arr.flatMap(fn);
-assert.compareArray(actual, arr, 'returns a similar array');
-assert.notSameValue(actual, arr, 'not the same array');
+assert.compareArray(actual, arr, 'The value of actual is expected to equal the value of arr');
+assert.notSameValue(actual, arr, 'The value of actual is expected to not equal the value of `arr`');
 
 var arrLike = {
   length: 4,
@@ -63,6 +63,10 @@ var arrLike = {
 };
 
 actual = [].flatMap.call(arrLike, fn);
-assert.compareArray(actual, [obj1, obj2, obj3, arrLike], 'returns a similar array');
-assert.notSameValue(actual, arrLike, 'not the same object');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype);
+assert.compareArray(actual, [obj1, obj2, obj3, arrLike], 'The value of actual is expected to be [obj1, obj2, obj3, arrLike]');
+assert.notSameValue(actual, arrLike, 'The value of actual is expected to not equal the value of `arrLike`');
+assert.sameValue(
+  Object.getPrototypeOf(actual),
+  Array.prototype,
+  'Object.getPrototypeOf([].flatMap.call(arrLike, fn)") returns Array.prototype'
+);
diff --git a/test/built-ins/Array/prototype/flatMap/array-like-objects-typedarrays.js b/test/built-ins/Array/prototype/flatMap/array-like-objects-typedarrays.js
index fd0dd5a192..f8e567a05b 100644
--- a/test/built-ins/Array/prototype/flatMap/array-like-objects-typedarrays.js
+++ b/test/built-ins/Array/prototype/flatMap/array-like-objects-typedarrays.js
@@ -35,9 +35,9 @@ Object.defineProperty(ta, 'constructor', {
   get() { throw "it should not object the typedarray ctor"; }
 });
 actual = [].flatMap.call(ta, same);
-assert.compareArray(actual, [1, 0, 42], 'compare returned array');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'returned object is an array #1');
-assert.sameValue(actual instanceof Int32Array, false, 'returned object is not an instance of Int32Array #1');
+assert.compareArray(actual, [1, 0, 42], 'The value of actual is expected to be [1, 0, 42]');
+assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'Object.getPrototypeOf([].flatMap.call(ta, same)") returns Array.prototype');
+assert.sameValue(actual instanceof Int32Array, false, 'The result of evaluating (actual instanceof Int32Array) is expected to be false');
 
 ta = new Int32Array(0);
 
@@ -45,6 +45,6 @@ Object.defineProperty(ta, 'constructor', {
   get() { throw "it should not object the typedarray ctor"; }
 });
 actual = [].flatMap.call(ta, same);
-assert.compareArray(actual, [], 'compare returned empty array');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'returned object is an array #2');
-assert.sameValue(actual instanceof Int32Array, false, 'returned object is not an instance of Int32Array #2');
+assert.compareArray(actual, [], 'The value of actual is expected to be []');
+assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'Object.getPrototypeOf([].flatMap.call(ta, same)") returns Array.prototype');
+assert.sameValue(actual instanceof Int32Array, false, 'The result of evaluating (actual instanceof Int32Array) is expected to be false');
diff --git a/test/built-ins/Array/prototype/flatMap/array-like-objects.js b/test/built-ins/Array/prototype/flatMap/array-like-objects.js
index 5a8a2fca33..6e33e968b9 100644
--- a/test/built-ins/Array/prototype/flatMap/array-like-objects.js
+++ b/test/built-ins/Array/prototype/flatMap/array-like-objects.js
@@ -47,16 +47,16 @@ a = {
   get 3() { throw 'it should not get this property'; }
 };
 actual = [].flatMap.call(a, fn);
-assert.compareArray(actual, [39, 2, 39, 42], 'array-like flattened object, number length');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'returned object is an array #1');
+assert.compareArray(actual, [39, 2, 39, 42], 'The value of actual is expected to be [39, 2, 39, 42]');
+assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'Object.getPrototypeOf([].flatMap.call(a, fn)") returns Array.prototype');
 
 a = {
   length: undefined,
   get 0() { throw 'it should not get this property'; },
 };
 actual = [].flatMap.call(a, fn);
-assert.compareArray(actual, [], 'array-like objects; undefined length');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'returned object is an array #2');
+assert.compareArray(actual, [], 'The value of actual is expected to be []');
+assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'Object.getPrototypeOf([].flatMap.call(a, fn)") returns Array.prototype');
 
 var called = false;
 a = {
@@ -73,13 +73,13 @@ a = {
   get 2() { throw 'it should not get this property'; },
 };
 actual = [].flatMap.call(a, fn);
-assert.compareArray(actual, [39, 42, 39, 39], 'array-like flattened objects; custom get length');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'returned object is an array #3');
+assert.compareArray(actual, [39, 42, 39, 39], 'The value of actual is expected to be [39, 42, 39, 39]');
+assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'Object.getPrototypeOf([].flatMap.call(a, fn)") returns Array.prototype');
 
 a = {
   length: 10001,
   [10000]: 7,
 };
 actual = [].flatMap.call(a, fn);
-assert.compareArray(actual, [39, 14], 'array-like flattened object, long length simulating shallow array');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'returned object is an array #4');
+assert.compareArray(actual, [39, 14], 'The value of actual is expected to be [39, 14]');
+assert.sameValue(Object.getPrototypeOf(actual), Array.prototype, 'Object.getPrototypeOf([].flatMap.call(a, fn)") returns Array.prototype');
diff --git a/test/built-ins/Array/prototype/flatMap/bound-function-argument.js b/test/built-ins/Array/prototype/flatMap/bound-function-argument.js
index daa3141157..898f43365e 100644
--- a/test/built-ins/Array/prototype/flatMap/bound-function-argument.js
+++ b/test/built-ins/Array/prototype/flatMap/bound-function-argument.js
@@ -11,4 +11,4 @@ features: [Array.prototype.flatMap]
 var a = [0, 0];
 assert.compareArray(a.flatMap(function() {
   return this;
-}.bind([1, 2])), [1, 2, 1, 2]);
+}.bind([1, 2])), [1, 2, 1, 2], 'a.flatMap(function() {return this;}.bind([1, 2])) must return [1, 2, 1, 2]');
diff --git a/test/built-ins/Array/prototype/flatMap/depth-always-one.js b/test/built-ins/Array/prototype/flatMap/depth-always-one.js
index 4f5f672b48..d372cff99c 100644
--- a/test/built-ins/Array/prototype/flatMap/depth-always-one.js
+++ b/test/built-ins/Array/prototype/flatMap/depth-always-one.js
@@ -10,14 +10,14 @@ features: [Array.prototype.flatMap]
 
 assert.compareArray([1, 2].flatMap(function(e) {
   return [e, e * 2];
-}), [1, 2, 2, 4], 'array depth is 1');
+}), [1, 2, 2, 4], '[1, 2].flatMap(function(e) {return [e, e * 2];}) must return [1, 2, 2, 4]');
 
 var result = [1, 2, 3].flatMap(function(ele) {
   return [
     [ele * 2]
   ];
 });
-assert.sameValue(result.length, 3, 'array depth is more than 1 - length');
-assert.compareArray(result[0], [2], 'array depth is more than 1 - 1st element');
-assert.compareArray(result[1], [4], 'array depth is more than 1 - 2nd element');
-assert.compareArray(result[2], [6], 'array depth is more than 1 - 3rd element');
+assert.sameValue(result.length, 3, 'The value of result.length is expected to be 3');
+assert.compareArray(result[0], [2], 'The value of result[0] is expected to be [2]');
+assert.compareArray(result[1], [4], 'The value of result[1] is expected to be [4]');
+assert.compareArray(result[2], [6], 'The value of result[2] is expected to be [6]');
diff --git a/test/built-ins/Array/prototype/flatMap/proxy-access-count.js b/test/built-ins/Array/prototype/flatMap/proxy-access-count.js
index 4e7edbd689..dbcf69122a 100644
--- a/test/built-ins/Array/prototype/flatMap/proxy-access-count.js
+++ b/test/built-ins/Array/prototype/flatMap/proxy-access-count.js
@@ -21,7 +21,11 @@ features: [Array.prototype.flatMap]
 includes: [compareArray.js]
 ---*/
 
-assert.sameValue(typeof Array.prototype.flatMap, 'function');
+assert.sameValue(
+  typeof Array.prototype.flatMap,
+  'function',
+  'The value of `typeof Array.prototype.flatMap` is expected to be "function"'
+);
 
 const getCalls = [], hasCalls = [];
 const handler = {
@@ -34,5 +38,5 @@ const tier1 = new Proxy([2, [3, 4, 2, 2], 5, tier2, 6], handler);
 
 Array.prototype.flatMap.call(tier1, function(a){ return a; });
 
-assert.compareArray(getCalls, ["length", "constructor", "0", "1", "2", "3", "length", "0", "1", "4"], 'getProperty by .flatMap should occur exactly once per property and once for length and constructor');
-assert.compareArray(hasCalls, ["0", "1", "2", "3", "0", "1", "4"], 'hasProperty by .flatMap should occur exactly once per property');
+assert.compareArray(getCalls, ["length", "constructor", "0", "1", "2", "3", "length", "0", "1", "4"], 'The value of getCalls is expected to be ["length", "constructor", "0", "1", "2", "3", "length", "0", "1", "4"]');
+assert.compareArray(hasCalls, ["0", "1", "2", "3", "0", "1", "4"], 'The value of hasCalls is expected to be ["0", "1", "2", "3", "0", "1", "4"]');
diff --git a/test/built-ins/Array/prototype/flatMap/this-value-ctor-non-object.js b/test/built-ins/Array/prototype/flatMap/this-value-ctor-non-object.js
index a71ad5a4ed..beabd126a1 100644
--- a/test/built-ins/Array/prototype/flatMap/this-value-ctor-non-object.js
+++ b/test/built-ins/Array/prototype/flatMap/this-value-ctor-non-object.js
@@ -32,7 +32,11 @@ features: [Array.prototype.flatMap, Symbol]
 includes: [compareArray.js]
 ---*/
 
-assert.sameValue(typeof Array.prototype.flatMap, 'function');
+assert.sameValue(
+  typeof Array.prototype.flatMap,
+  'function',
+  'The value of `typeof Array.prototype.flatMap` is expected to be "function"'
+);
 
 var a = [];
 var mapperFn = function() {};
@@ -40,35 +44,39 @@ var mapperFn = function() {};
 a.constructor = null;
 assert.throws(TypeError, function() {
   a.flatMap(mapperFn);
-}, 'null value');
+}, 'a.flatMap(mapperFn) throws a TypeError exception');
 
 a = [];
 a.constructor = 1;
 assert.throws(TypeError, function() {
   a.flatMap(mapperFn);
-}, 'number value');
+}, 'a.flatMap(mapperFn) throws a TypeError exception');
 
 a = [];
 a.constructor = 'string';
 assert.throws(TypeError, function() {
   a.flatMap(mapperFn);
-}, 'string value');
+}, 'a.flatMap(mapperFn) throws a TypeError exception');
 
 a = [];
 a.constructor = true;
 assert.throws(TypeError, function() {
   a.flatMap(mapperFn);
-}, 'boolean value');
+}, 'a.flatMap(mapperFn) throws a TypeError exception');
 
 a = [];
 a.constructor = Symbol();
 assert.throws(TypeError, function() {
   a.flatMap(mapperFn);
-}, 'symbol value');
+}, 'a.flatMap(mapperFn) throws a TypeError exception');
 
 a = [];
 a.constructor = undefined;
 var actual = a.flatMap(mapperFn);
-assert.compareArray(actual, [], 'undefined value does not throw');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype);
-assert.notSameValue(actual, a, 'returns a new array');
+assert.compareArray(actual, [], 'The value of actual is expected to be []');
+assert.sameValue(
+  Object.getPrototypeOf(actual),
+  Array.prototype,
+  'Object.getPrototypeOf(a.flatMap(mapperFn)) returns Array.prototype'
+);
+assert.notSameValue(actual, a, 'The value of actual is expected to not equal the value of `a`');
diff --git a/test/built-ins/Array/prototype/flatMap/this-value-ctor-object-species-bad-throws.js b/test/built-ins/Array/prototype/flatMap/this-value-ctor-object-species-bad-throws.js
index 9ea5f2a02b..c5d97cef12 100644
--- a/test/built-ins/Array/prototype/flatMap/this-value-ctor-object-species-bad-throws.js
+++ b/test/built-ins/Array/prototype/flatMap/this-value-ctor-object-species-bad-throws.js
@@ -34,15 +34,23 @@ features: [Array.prototype.flatMap, Symbol, Symbol.species]
 includes: [compareArray.js]
 ---*/
 
-assert.sameValue(typeof Array.prototype.flatMap, 'function');
+assert.sameValue(
+  typeof Array.prototype.flatMap,
+  'function',
+  'The value of `typeof Array.prototype.flatMap` is expected to be "function"'
+);
 
 var arr = [[42, 1], [42, 2]];
 var mapperFn = function(e) { return e; };
 
 arr.constructor = {};
 var actual = arr.flatMap(mapperFn);
-assert.compareArray(actual, [42, 1, 42, 2], 'undefined species does not throw');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype);
+assert.compareArray(actual, [42, 1, 42, 2], 'The value of actual is expected to be [42, 1, 42, 2]');
+assert.sameValue(
+  Object.getPrototypeOf(actual),
+  Array.prototype,
+  'Object.getPrototypeOf(arr.flatMap(mapperFn)) returns Array.prototype'
+);
 
 var called = 0;
 arr.constructor = {
@@ -53,8 +61,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is a number');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -65,8 +73,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is a string');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -77,8 +85,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is a boolean');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -89,8 +97,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is an object');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -101,8 +109,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is an array');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -113,8 +121,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is a symbol');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -125,5 +133,5 @@ arr.constructor = {
 };
 assert.throws(Test262Error, function() {
   arr.flatMap(mapperFn);
-}, 'Return abrupt completion from getting the @@species');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a Test262Error exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
diff --git a/test/built-ins/Array/prototype/flatMap/this-value-ctor-object-species.js b/test/built-ins/Array/prototype/flatMap/this-value-ctor-object-species.js
index a8d560bff2..1b48ee4737 100644
--- a/test/built-ins/Array/prototype/flatMap/this-value-ctor-object-species.js
+++ b/test/built-ins/Array/prototype/flatMap/this-value-ctor-object-species.js
@@ -34,15 +34,23 @@ features: [Array.prototype.flatMap, Symbol, Symbol.species]
 includes: [compareArray.js]
 ---*/
 
-assert.sameValue(typeof Array.prototype.flatMap, 'function');
+assert.sameValue(
+  typeof Array.prototype.flatMap,
+  'function',
+  'The value of `typeof Array.prototype.flatMap` is expected to be "function"'
+);
 
 var arr = [[42, 1], [42, 2]];
 var mapperFn = function(e) { return e; };
 
 arr.constructor = {};
 var actual = arr.flatMap(mapperFn);
-assert.compareArray(actual, [42, 1, 42, 2], 'undefined species does not throw');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype);
+assert.compareArray(actual, [42, 1, 42, 2], 'The value of actual is expected to be [42, 1, 42, 2]');
+assert.sameValue(
+  Object.getPrototypeOf(actual),
+  Array.prototype,
+  'Object.getPrototypeOf(arr.flatMap(mapperFn)) returns Array.prototype'
+);
 
 var called = 0;
 arr.constructor = {
@@ -52,9 +60,13 @@ arr.constructor = {
   }
 };
 actual = arr.flatMap(mapperFn);
-assert.compareArray(actual, [42, 1, 42, 2], 'null species value does not throw');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype);
-assert.sameValue(called, 1, 'got species once');
+assert.compareArray(actual, [42, 1, 42, 2], 'The value of actual is expected to be [42, 1, 42, 2]');
+assert.sameValue(
+  Object.getPrototypeOf(actual),
+  Array.prototype,
+  'Object.getPrototypeOf(arr.flatMap(mapperFn)) returns Array.prototype'
+);
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -64,9 +76,13 @@ arr.constructor = {
   }
 };
 actual = arr.flatMap(mapperFn);
-assert.compareArray(actual, [42, 1, 42, 2], 'undefined species value does not throw');
-assert.sameValue(Object.getPrototypeOf(actual), Array.prototype);
-assert.sameValue(called, 1, 'got species once');
+assert.compareArray(actual, [42, 1, 42, 2], 'The value of actual is expected to be [42, 1, 42, 2]');
+assert.sameValue(
+  Object.getPrototypeOf(actual),
+  Array.prototype,
+  'Object.getPrototypeOf(arr.flatMap(mapperFn)) returns Array.prototype'
+);
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -77,8 +93,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is a number');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -89,8 +105,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is a string');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -101,8 +117,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is a boolean');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -113,8 +129,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is an object');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -125,8 +141,8 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is an array');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
 
 called = 0;
 arr.constructor = {
@@ -137,5 +153,5 @@ arr.constructor = {
 };
 assert.throws(TypeError, function() {
   arr.flatMap(mapperFn);
-}, 'throw TypeError if @@species is a symbol');
-assert.sameValue(called, 1, 'got species once');
+}, 'arr.flatMap(mapperFn) throws a TypeError exception');
+assert.sameValue(called, 1, 'The value of called is expected to be 1');
diff --git a/test/built-ins/Array/prototype/flatMap/thisArg-argument.js b/test/built-ins/Array/prototype/flatMap/thisArg-argument.js
index 24b52af747..835e384f53 100644
--- a/test/built-ins/Array/prototype/flatMap/thisArg-argument.js
+++ b/test/built-ins/Array/prototype/flatMap/thisArg-argument.js
@@ -16,30 +16,30 @@ var actual;
 actual = [1].flatMap(function() {
   return [this];
 }, "TestString");
-assert.compareArray(actual, ["TestString"]);
+assert.compareArray(actual, ["TestString"], 'The value of actual is expected to be ["TestString"]');
 
 actual = [1].flatMap(function() {
   return [this];
 }, 1);
-assert.compareArray(actual, [1]);
+assert.compareArray(actual, [1], 'The value of actual is expected to be [1]');
 
 actual = [1].flatMap(function() {
   return [this];
 }, null);
-assert.compareArray(actual, [null]);
+assert.compareArray(actual, [null], 'The value of actual is expected to be [null]');
 
 actual = [1].flatMap(function() {
   return [this];
 }, true);
-assert.compareArray(actual, [true]);
+assert.compareArray(actual, [true], 'The value of actual is expected to be [true]');
 
 actual = [1].flatMap(function() {
   return [this];
 }, a);
-assert.compareArray(actual, [a]);
+assert.compareArray(actual, [a], 'The value of actual is expected to be [a]');
 
 actual = [1].flatMap(function() {
   return [this];
 }, void 0);
-assert.compareArray(actual, [undefined]);
+assert.compareArray(actual, [undefined], 'The value of actual is expected to be [undefined]');
 
diff --git a/test/built-ins/Array/prototype/includes/get-prop.js b/test/built-ins/Array/prototype/includes/get-prop.js
index 069b77a298..bea3d5a9af 100644
--- a/test/built-ins/Array/prototype/includes/get-prop.js
+++ b/test/built-ins/Array/prototype/includes/get-prop.js
@@ -32,12 +32,15 @@ var p = new Proxy(obj, {
 });
 
 calls = [];
-assert.sameValue([].includes.call(p, 42), false);
-assert(
-  compareArray(calls, ["length", "0", "1", "2", "3"]),
-  "loops through all indexes"
+assert.sameValue(
+  [].includes.call(p, 42),
+  false,
+  '[].includes.call("new Proxy(obj, {get: function(_, key) {calls.push(key); if (key === "length") {return 4;} return key * 10;}})", 42) must return false'
+);
+assert.compareArray(calls, ["length", "0", "1", "2", "3"],
+  'The value of calls is expected to be ["length", "0", "1", "2", "3"]'
 );
 
 calls = [];
-assert.sameValue([].includes.call(p, 10), true, "uses the returned value");
-assert(compareArray(calls, ["length", "0", "1"]), "loops until value is found");
+assert.sameValue([].includes.call(p, 10), true, '[].includes.call("new Proxy(obj, {get: function(_, key) {calls.push(key); if (key === "length") {return 4;} return key * 10;}})", 10) must return true');
+assert.compareArray(calls, ["length", "0", "1"], 'The value of calls is expected to be ["length", "0", "1"]');
diff --git a/test/built-ins/Array/prototype/reduceRight/length-near-integer-limit.js b/test/built-ins/Array/prototype/reduceRight/length-near-integer-limit.js
index f955b66e62..9d297caddb 100644
--- a/test/built-ins/Array/prototype/reduceRight/length-near-integer-limit.js
+++ b/test/built-ins/Array/prototype/reduceRight/length-near-integer-limit.js
@@ -43,7 +43,15 @@ try {
   Array.prototype.reduceRight.call(arrayLike, accumulator, []);
   throw new Test262Error("should not be called");
 } catch (acc) {
-  assert.sameValue(acc.length, 2);
-  assert.compareArray(acc[0], [1, Number.MAX_SAFE_INTEGER - 1]);
-  assert.compareArray(acc[1], [3, Number.MAX_SAFE_INTEGER - 3]);
+  assert.sameValue(acc.length, 2, 'The value of acc.length is expected to be 2');
+  assert.compareArray(
+    acc[0],
+    [1, Number.MAX_SAFE_INTEGER - 1],
+    'The value of acc[0] is expected to be [1, Number.MAX_SAFE_INTEGER - 1]'
+  );
+  assert.compareArray(
+    acc[1],
+    [3, Number.MAX_SAFE_INTEGER - 3],
+    'The value of acc[1] is expected to be [3, Number.MAX_SAFE_INTEGER - 3]'
+  );
 }
diff --git a/test/built-ins/Array/prototype/reverse/length-exceeding-integer-limit-with-proxy.js b/test/built-ins/Array/prototype/reverse/length-exceeding-integer-limit-with-proxy.js
index 308eb5e192..f827f9f162 100644
--- a/test/built-ins/Array/prototype/reverse/length-exceeding-integer-limit-with-proxy.js
+++ b/test/built-ins/Array/prototype/reverse/length-exceeding-integer-limit-with-proxy.js
@@ -61,7 +61,7 @@ var proxy = new Proxy(arrayLike, allowProxyTraps({
 // are properly propagated.
 assert.throws(StopReverse, function() {
   Array.prototype.reverse.call(proxy);
-});
+}, 'Array.prototype.reverse.call(proxy) throws a StopReverse exception');
 
 assert.compareArray(traps, [
   // Initial get length operation.
@@ -104,16 +104,16 @@ assert.compareArray(traps, [
   // Stop exception.
   "Has:4",
   "Get:4",
-]);
+], 'The value of traps is expected to be [\n  // Initial get length operation.\n  "Get:length",\n\n  // Lower and upper index are both present.\n  "Has:0",\n  "Get:0",\n  "Has:9007199254740990",\n  "Get:9007199254740990",\n  "Set:0",\n  "GetOwnPropertyDescriptor:0",\n  "DefineProperty:0",\n  "Set:9007199254740990",\n  "GetOwnPropertyDescriptor:9007199254740990",\n  "DefineProperty:9007199254740990",\n\n  // Lower and upper index are both absent.\n  "Has:1",\n  "Has:9007199254740989",\n\n  // Lower index is present, upper index is absent.\n  "Has:2",\n  "Get:2",\n  "Has:9007199254740988",\n  "Delete:2",\n  "Set:9007199254740988",\n  "GetOwnPropertyDescriptor:9007199254740988",\n  "DefineProperty:9007199254740988",\n\n  // Lower index is absent, upper index is present.\n  "Has:3",\n  "Has:9007199254740987",\n  "Get:9007199254740987",\n  "Set:3",\n  "GetOwnPropertyDescriptor:3",\n  "DefineProperty:3",\n  "Delete:9007199254740987",\n\n  // Stop exception.\n  "Has:4",\n  "Get:4",\n]');
 
-assert.sameValue(arrayLike.length, 2 ** 53 + 2, "Length property is not modified");
+assert.sameValue(arrayLike.length, 2 ** 53 + 2, 'The value of arrayLike.length is expected to be 2 ** 53 + 2');
 
-assert.sameValue(arrayLike[0], "2**53-2", "Property at index 0");
-assert.sameValue(1 in arrayLike, false, "Property at index 1");
-assert.sameValue(2 in arrayLike, false, "Property at index 2");
-assert.sameValue(arrayLike[3], "2**53-5", "Property at index 3");
+assert.sameValue(arrayLike[0], "2**53-2", 'The value of arrayLike[0] is expected to be "2**53-2"');
+assert.sameValue(1 in arrayLike, false, 'The result of evaluating (1 in arrayLike) is expected to be false');
+assert.sameValue(2 in arrayLike, false, 'The result of evaluating (2 in arrayLike) is expected to be false');
+assert.sameValue(arrayLike[3], "2**53-5", 'The value of arrayLike[3] is expected to be "2**53-5"');
 
-assert.sameValue(9007199254740987 in arrayLike, false, "Property at index 2**53-5");
-assert.sameValue(arrayLike[9007199254740988], "two", "Property at index 2**53-4");
-assert.sameValue(9007199254740989 in arrayLike, false, "Property at index 2**53-3");
-assert.sameValue(arrayLike[9007199254740990], "zero", "Property at index 2**53-2");
+assert.sameValue(9007199254740987 in arrayLike, false, 'The result of evaluating (9007199254740987 in arrayLike) is expected to be false');
+assert.sameValue(arrayLike[9007199254740988], "two", 'The value of arrayLike[9007199254740988] is expected to be "two"');
+assert.sameValue(9007199254740989 in arrayLike, false, 'The result of evaluating (9007199254740989 in arrayLike) is expected to be false');
+assert.sameValue(arrayLike[9007199254740990], "zero", 'The value of arrayLike[9007199254740990] is expected to be "zero"');
diff --git a/test/built-ins/Array/prototype/slice/length-exceeding-integer-limit-proxied-array.js b/test/built-ins/Array/prototype/slice/length-exceeding-integer-limit-proxied-array.js
index d1839760a1..79ca743e08 100644
--- a/test/built-ins/Array/prototype/slice/length-exceeding-integer-limit-proxied-array.js
+++ b/test/built-ins/Array/prototype/slice/length-exceeding-integer-limit-proxied-array.js
@@ -37,20 +37,20 @@ var proxy = new Proxy(array, {
 
 var result = Array.prototype.slice.call(proxy, 9007199254740989);
 assert.compareArray(result, ["9007199254740989", "9007199254740990"],
-  "slice(9007199254740989)");
+  'The value of result is expected to be ["9007199254740989", "9007199254740990"]');
 
 var result = Array.prototype.slice.call(proxy, 9007199254740989, 9007199254740990);
 assert.compareArray(result, ["9007199254740989"],
-  "slice(9007199254740989, 9007199254740990)");
+  'The value of result is expected to be ["9007199254740989"]');
 
 var result = Array.prototype.slice.call(proxy, 9007199254740989, 9007199254740996);
 assert.compareArray(result, ["9007199254740989", "9007199254740990"],
-  "slice(9007199254740989, 9007199254740996)");
+  'The value of result is expected to be ["9007199254740989", "9007199254740990"]');
 
 var result = Array.prototype.slice.call(proxy, -2);
 assert.compareArray(result, ["9007199254740989", "9007199254740990"],
-  "slice(-2)");
+  'The value of result is expected to be ["9007199254740989", "9007199254740990"]');
 
 var result = Array.prototype.slice.call(proxy, -2, -1);
 assert.compareArray(result, ["9007199254740989"],
-  "slice(-2, -1)");
+  'The value of result is expected to be ["9007199254740989"]');
diff --git a/test/built-ins/Array/prototype/slice/length-exceeding-integer-limit.js b/test/built-ins/Array/prototype/slice/length-exceeding-integer-limit.js
index d3b4292881..7adf639c7b 100644
--- a/test/built-ins/Array/prototype/slice/length-exceeding-integer-limit.js
+++ b/test/built-ins/Array/prototype/slice/length-exceeding-integer-limit.js
@@ -28,20 +28,20 @@ var arrayLike = {
 
 var result = Array.prototype.slice.call(arrayLike, 9007199254740989);
 assert.compareArray(result, ["9007199254740989", "9007199254740990"],
-  "slice(9007199254740989)");
+  'The value of result is expected to be ["9007199254740989", "9007199254740990"]');
 
 var result = Array.prototype.slice.call(arrayLike, 9007199254740989, 9007199254740990);
 assert.compareArray(result, ["9007199254740989"],
-  "slice(9007199254740989, 9007199254740990)");
+  'The value of result is expected to be ["9007199254740989"]');
 
 var result = Array.prototype.slice.call(arrayLike, 9007199254740989, 9007199254740996);
 assert.compareArray(result, ["9007199254740989", "9007199254740990"],
-  "slice(9007199254740989, 9007199254740996)");
+  'The value of result is expected to be ["9007199254740989", "9007199254740990"]');
 
 var result = Array.prototype.slice.call(arrayLike, -2);
 assert.compareArray(result, ["9007199254740989", "9007199254740990"],
-  "slice(-2)");
+  'The value of result is expected to be ["9007199254740989", "9007199254740990"]');
 
 var result = Array.prototype.slice.call(arrayLike, -2, -1);
 assert.compareArray(result, ["9007199254740989"],
-  "slice(-2, -1)");
+  'The value of result is expected to be ["9007199254740989"]');
diff --git a/test/built-ins/Array/prototype/splice/create-species-length-exceeding-integer-limit.js b/test/built-ins/Array/prototype/splice/create-species-length-exceeding-integer-limit.js
index f0a5d73ed5..2efecc76b7 100644
--- a/test/built-ins/Array/prototype/splice/create-species-length-exceeding-integer-limit.js
+++ b/test/built-ins/Array/prototype/splice/create-species-length-exceeding-integer-limit.js
@@ -67,10 +67,10 @@ var target = new Proxy([], allowProxyTraps({
 assert.throws(StopSplice, function() {
   // deleteCount argument exceeding 2^53-1.
   Array.prototype.splice.call(source, 0, 2 ** 53 + 4);
-});
+}, '// deleteCount argument exceeding 2^53-1. Array.prototype.splice.call(source, 0, 2 ** 53 + 4) throws a StopSplice exception');
 
 assert.sameValue(targetLength, 2 ** 53 - 1,
-  "length and deleteCount were correctly clamped to 2^53-1");
+  'The value of targetLength is expected to be 2 ** 53 - 1');
 
 assert.compareArray(traps, [
   "source.[[Get]]:length",
@@ -86,4 +86,4 @@ assert.compareArray(traps, [
   "source.[[Has]]:2",
   "source.[[Get]]:2",
   "target.[[DefineProperty]]:2",
-]);
+], 'The value of traps is expected to be [\n  "source.[[Get]]:length",\n\n  "source.[[Get]]:constructor",\n\n  "source.[[Has]]:0",\n  "source.[[Get]]:0",\n  "target.[[DefineProperty]]:0",\n\n  "source.[[Has]]:1",\n\n  "source.[[Has]]:2",\n  "source.[[Get]]:2",\n  "target.[[DefineProperty]]:2",\n]');
diff --git a/test/built-ins/Array/prototype/splice/length-and-deleteCount-exceeding-integer-limit.js b/test/built-ins/Array/prototype/splice/length-and-deleteCount-exceeding-integer-limit.js
index 7734bb325a..3c68671237 100644
--- a/test/built-ins/Array/prototype/splice/length-and-deleteCount-exceeding-integer-limit.js
+++ b/test/built-ins/Array/prototype/splice/length-and-deleteCount-exceeding-integer-limit.js
@@ -36,19 +36,19 @@ var arrayLike = {
 var result = Array.prototype.splice.call(arrayLike, 9007199254740989, 2 ** 53 + 4);
 
 assert.compareArray(result, ["9007199254740989", "9007199254740990"],
-  "arrayLike['9007199254740989'] and arrayLike['9007199254740990'] are removed");
+  'The value of result is expected to be ["9007199254740989", "9007199254740990"]');
 
 assert.sameValue(arrayLike.length, 2 ** 53 - 3,
-  "New length is 2**53 - 3");
+  'The value of arrayLike.length is expected to be 2 ** 53 - 3');
 
 assert.sameValue(arrayLike["9007199254740988"], "9007199254740988",
-  "arrayLike['9007199254740988'] is unchanged");
+  'The value of arrayLike["9007199254740988"] is expected to be "9007199254740988"');
 
 assert.sameValue("9007199254740989" in arrayLike, false,
-  "arrayLike['9007199254740989'] is removed");
+  'The result of evaluating ("9007199254740989" in arrayLike) is expected to be false');
 
 assert.sameValue("9007199254740990" in arrayLike, false,
-  "arrayLike['9007199254740990'] is removed");
+  'The result of evaluating ("9007199254740990" in arrayLike) is expected to be false');
 
 assert.sameValue(arrayLike["9007199254740991"], "9007199254740991",
-  "arrayLike['9007199254740991'] is unchanged");
+  'The value of arrayLike["9007199254740991"] is expected to be "9007199254740991"');
diff --git a/test/built-ins/Array/prototype/splice/length-exceeding-integer-limit-shrink-array.js b/test/built-ins/Array/prototype/splice/length-exceeding-integer-limit-shrink-array.js
index 8340b6a29e..46a59a25f2 100644
--- a/test/built-ins/Array/prototype/splice/length-exceeding-integer-limit-shrink-array.js
+++ b/test/built-ins/Array/prototype/splice/length-exceeding-integer-limit-shrink-array.js
@@ -40,25 +40,25 @@ var arrayLike = {
 var result = Array.prototype.splice.call(arrayLike, 9007199254740987, 1);
 
 assert.compareArray(result, ["9007199254740987"],
-  "arrayLike['9007199254740987'] is removed");
+  'The value of result is expected to be ["9007199254740987"]');
 
 assert.sameValue(arrayLike.length, 2 ** 53 - 2,
-  "New length is 2**53 - 2");
+  'The value of arrayLike.length is expected to be 2 ** 53 - 2');
 
 assert.sameValue(arrayLike["9007199254740986"], "9007199254740986",
-  "arrayLike['9007199254740986'] is unchanged");
+  'The value of arrayLike["9007199254740986"] is expected to be "9007199254740986"');
 
 assert.sameValue(arrayLike["9007199254740987"], "9007199254740988",
-  "arrayLike['9007199254740988'] is moved to arrayLike['9007199254740987']");
+  'The value of arrayLike["9007199254740987"] is expected to be "9007199254740988"');
 
 assert.sameValue("9007199254740988" in arrayLike, false,
-  "arrayLike['9007199254740990'] is removed");
+  'The result of evaluating ("9007199254740988" in arrayLike) is expected to be false');
 
 assert.sameValue(arrayLike["9007199254740989"], "9007199254740990",
-  "arrayLike['9007199254740990'] is moved to arrayLike['9007199254740989']");
+  'The value of arrayLike["9007199254740989"] is expected to be "9007199254740990"');
 
 assert.sameValue("9007199254740990" in arrayLike, false,
-  "arrayLike['9007199254740990'] is removed");
+  'The result of evaluating ("9007199254740990" in arrayLike) is expected to be false');
 
 assert.sameValue(arrayLike["9007199254740991"], "9007199254740991",
-  "arrayLike['9007199254740991'] is unchanged");
+  'The value of arrayLike["9007199254740991"] is expected to be "9007199254740991"');
diff --git a/test/built-ins/Array/prototype/splice/length-near-integer-limit-grow-array.js b/test/built-ins/Array/prototype/splice/length-near-integer-limit-grow-array.js
index 42cf6f9c50..a36b385a61 100644
--- a/test/built-ins/Array/prototype/splice/length-near-integer-limit-grow-array.js
+++ b/test/built-ins/Array/prototype/splice/length-near-integer-limit-grow-array.js
@@ -36,27 +36,27 @@ var arrayLike = {
 
 var result = Array.prototype.splice.call(arrayLike, 9007199254740986, 0, "new-value");
 
-assert.compareArray(result, [], "No elements are removed");
+assert.compareArray(result, [], 'The value of result is expected to be []');
 
-assert.sameValue(arrayLike.length, 2 ** 53 - 1, "New length is 2**53 - 1");
+assert.sameValue(arrayLike.length, 2 ** 53 - 1, 'The value of arrayLike.length is expected to be 2 ** 53 - 1');
 
 assert.sameValue(arrayLike["9007199254740985"], "9007199254740985",
-  "arrayLike['9007199254740985'] is unchanged");
+  'The value of arrayLike["9007199254740985"] is expected to be "9007199254740985"');
 
 assert.sameValue(arrayLike["9007199254740986"], "new-value",
-  "arrayLike['9007199254740986'] contains the inserted value");
+  'The value of arrayLike["9007199254740986"] is expected to be "new-value"');
 
 assert.sameValue(arrayLike["9007199254740987"], "9007199254740986",
-  "arrayLike['9007199254740986'] is moved to arrayLike['9007199254740987']");
+  'The value of arrayLike["9007199254740987"] is expected to be "9007199254740986"');
 
 assert.sameValue(arrayLike["9007199254740988"], "9007199254740987",
-  "arrayLike['9007199254740987'] is moved to arrayLike['9007199254740988']");
+  'The value of arrayLike["9007199254740988"] is expected to be "9007199254740987"');
 
 assert.sameValue("9007199254740989" in arrayLike, false,
-  "arrayLike['9007199254740989'] is removed");
+  'The result of evaluating ("9007199254740989" in arrayLike) is expected to be false');
 
 assert.sameValue(arrayLike["9007199254740990"], "9007199254740989",
-  "arrayLike['9007199254740989'] is moved to arrayLike['9007199254740990']");
+  'The value of arrayLike["9007199254740990"] is expected to be "9007199254740989"');
 
 assert.sameValue(arrayLike["9007199254740991"], "9007199254740991",
-  "arrayLike['9007199254740991'] is unchanged");
+  'The value of arrayLike["9007199254740991"] is expected to be "9007199254740991"');