diff --git a/harness/compareArray.js b/harness/compareArray.js
index adf294b5e8..f5d3169d62 100644
--- a/harness/compareArray.js
+++ b/harness/compareArray.js
@@ -26,8 +26,8 @@ compareArray.isSameValue = function(a, b) {
   return a === b;
 };
 
-compareArray.format = function(array) {
-  return `[${array.map(String).join(', ')}]`;
+compareArray.format = function(arrayLike) {
+  return `[${[].map.call(arrayLike, String).join(', ')}]`;
 };
 
 assert.compareArray = function(actual, expected, message) {
@@ -35,8 +35,11 @@ assert.compareArray = function(actual, expected, message) {
   assert(actual != null, `First argument shouldn't be nullish. ${message}`);
   assert(expected != null, `Second argument shouldn't be nullish. ${message}`);
   var format = compareArray.format;
-  assert(
-    compareArray(actual, expected),
-    `Expected ${format(actual)} and ${format(expected)} to have the same contents. ${message}`
-  );
+  var result = compareArray(actual, expected);
+
+  // The following prevents actual and expected from being iterated and evaluated
+  // more than once unless absolutely necessary.
+  if (!result) {
+    assert(false, `Expected ${format(actual)} and ${format(expected)} to have the same contents. ${message}`);
+  }
 };
diff --git a/test/harness/compare-array-arguments.js b/test/harness/compare-array-arguments.js
new file mode 100644
index 0000000000..597efa0564
--- /dev/null
+++ b/test/harness/compare-array-arguments.js
@@ -0,0 +1,38 @@
+// Copyright (C) 2021 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Accepts spreadable arguments
+includes: [compareArray.js]
+---*/
+
+const fixture = [0, 'a', undefined];
+
+function checkFormatOfAssertionMessage(func, errorMessage) {
+  var caught = false;
+  try {
+      func();
+  } catch (error) {
+      caught = true;
+      assert.sameValue(error.constructor, Test262Error);
+      assert.sameValue(error.message, errorMessage);
+  }
+
+  assert(caught, `Expected ${func} to throw, but it didn't.`);
+}
+
+function f() {
+  assert.compareArray(arguments, fixture);
+  assert.compareArray(fixture, arguments);
+
+  checkFormatOfAssertionMessage(() => {
+    assert.compareArray(arguments, [], 'arguments and []');
+  }, 'Expected [0, a, undefined] and [] to have the same contents. arguments and []');
+
+  checkFormatOfAssertionMessage(() => {
+    assert.compareArray([], arguments, '[] and arguments');
+  }, 'Expected [] and [0, a, undefined] to have the same contents. [] and arguments');
+}
+
+f(...fixture);
diff --git a/test/harness/compare-array-arraylike.js b/test/harness/compare-array-arraylike.js
new file mode 100644
index 0000000000..8318e5ff51
--- /dev/null
+++ b/test/harness/compare-array-arraylike.js
@@ -0,0 +1,34 @@
+// Copyright (C) 2021 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Accepts spreadable arguments
+includes: [compareArray.js]
+---*/
+
+function checkFormatOfAssertionMessage(func, errorMessage) {
+  var caught = false;
+  try {
+      func();
+  } catch (error) {
+      caught = true;
+      assert.sameValue(error.constructor, Test262Error);
+      assert.sameValue(error.message, errorMessage);
+  }
+
+  assert(caught, `Expected ${func} to throw, but it didn't.`);
+}
+
+const fixture = { length: 3, 0: 0, 1: 'a', 2: undefined};
+
+assert.compareArray(fixture, [0, 'a', undefined]);
+assert.compareArray([0, 'a', undefined], fixture);
+
+checkFormatOfAssertionMessage(() => {
+  assert.compareArray(fixture, [], 'fixture and []');
+}, 'Expected [0, a, undefined] and [] to have the same contents. fixture and []');
+
+checkFormatOfAssertionMessage(() => {
+  assert.compareArray([], fixture, '[] and fixture');
+}, 'Expected [] and [0, a, undefined] to have the same contents. [] and fixture');
diff --git a/test/harness/compare-array-different-elements.js b/test/harness/compare-array-different-elements.js
index 7519d96a9d..ef72d10d4a 100644
--- a/test/harness/compare-array-different-elements.js
+++ b/test/harness/compare-array-different-elements.js
@@ -10,6 +10,6 @@ includes: [compareArray.js]
 var first = [0, 'a', undefined];
 var second = [0, 'b', undefined];
 
-if (compareArray(first, second) !== false) {
-  throw new Error('Arrays containing different elements are not equivalent.');
-}
+assert.throws(Test262Error, () => {
+  assert.compareArray(first, second);
+}, 'Arrays containing different elements are not equivalent.');
diff --git a/test/harness/compare-array-different-length.js b/test/harness/compare-array-different-length.js
index a188fc2628..05debda822 100644
--- a/test/harness/compare-array-different-length.js
+++ b/test/harness/compare-array-different-length.js
@@ -7,10 +7,11 @@ description: >
 includes: [compareArray.js]
 ---*/
 
-if (compareArray([], [undefined]) !== false) {
-  throw new Error('Arrays of differing lengths are not equivalent.');
-}
 
-if (compareArray([undefined], []) !== false) {
-  throw new Error('Arrays of differing lengths are not equivalent.');
-}
+assert.throws(Test262Error, () => {
+  assert.compareArray([], [undefined]);
+}, 'Arrays of differing lengths are not equivalent.');
+
+assert.throws(Test262Error, () => {
+  assert.compareArray([undefined], []);
+}, 'Arrays of differing lengths are not equivalent.');
diff --git a/test/harness/compare-array-empty.js b/test/harness/compare-array-empty.js
index af701fd418..8a441f9bd0 100644
--- a/test/harness/compare-array-empty.js
+++ b/test/harness/compare-array-empty.js
@@ -7,6 +7,4 @@ description: >
 includes: [compareArray.js]
 ---*/
 
-if (compareArray([], []) !== true) {
-  throw new Error('Empty arrays are equivalent.');
-}
+assert.compareArray([], [], 'Empty arrays are equivalent.');
diff --git a/test/harness/compare-array-same-elements-different-order.js b/test/harness/compare-array-same-elements-different-order.js
index aa384c7cb7..369a32c456 100644
--- a/test/harness/compare-array-same-elements-different-order.js
+++ b/test/harness/compare-array-same-elements-different-order.js
@@ -11,6 +11,6 @@ var obj = {};
 var first = [0, 1, '', 's', null, undefined, obj];
 var second = [0, 1, '', 's', undefined, null, obj];
 
-if (compareArray(first, second) !== false) {
-  throw new Error('Arrays containing the same elements in different order are not equivalent.');
-}
+assert.throws(Test262Error, () => {
+  assert.compareArray(first, second);
+}, 'Arrays containing the same elements in different order are not equivalent.');
diff --git a/test/harness/compare-array-same-elements-same-order.js b/test/harness/compare-array-same-elements-same-order.js
index e363528ff7..a7fbc67807 100644
--- a/test/harness/compare-array-same-elements-same-order.js
+++ b/test/harness/compare-array-same-elements-same-order.js
@@ -11,6 +11,4 @@ var obj = {};
 var first = [0, 1, '', 's', undefined, null, obj];
 var second = [0, 1, '', 's', undefined, null, obj];
 
-if (compareArray(first, second) !== true) {
-  throw new Error('Arrays containing the same elements in the same order are equivalent.');
-}
+assert.compareArray(first, second, 'Arrays containing the same elements in the same order are equivalent.');
diff --git a/test/harness/compare-array-samevalue.js b/test/harness/compare-array-samevalue.js
index 826840e219..440dca3756 100644
--- a/test/harness/compare-array-samevalue.js
+++ b/test/harness/compare-array-samevalue.js
@@ -7,5 +7,7 @@ description: >
 includes: [compareArray.js]
 ---*/
 
-assert(compareArray([NaN], [NaN]));
-assert(!compareArray([0], [-0]));
+assert.compareArray([NaN], [NaN]);
+assert.throws(Test262Error, () => {
+  assert.compareArray([0], [-0]);
+});
diff --git a/test/harness/compare-array-sparse.js b/test/harness/compare-array-sparse.js
index ce2f4ae4f2..448a00e11a 100644
--- a/test/harness/compare-array-sparse.js
+++ b/test/harness/compare-array-sparse.js
@@ -7,22 +7,17 @@ description: >
 includes: [compareArray.js]
 ---*/
 
-if (compareArray([,], [,]) !== true) {
-  throw new Error('Sparse arrays of the same length are equivalent.');
-}
 
-if (compareArray([,], [,,]) !== false) {
-  throw new Error('Sparse arrays of differing lengths are not equivalent.');
-}
-
-if (compareArray([,,], [,]) !== false) {
-  throw new Error('Sparse arrays of differing lengths are not equivalent.');
-}
-
-if (compareArray([,], []) !== false) {
-  throw new Error('Sparse arrays are not equivalent to empty arrays.');
-}
-
-if (compareArray([], [,]) !== false) {
-  throw new Error('Sparse arrays are not equivalent to empty arrays.');
-}
+assert.compareArray([,], [,], 'Sparse arrays of the same length are equivalent.');
+assert.throws(Test262Error, () => {
+  assert.compareArray([,], [,,]);
+}, 'Sparse arrays of differing lengths are not equivalent.');
+assert.throws(Test262Error, () => {
+  assert.compareArray([,,], [,]);
+}, 'Sparse arrays of differing lengths are not equivalent.');
+assert.throws(Test262Error, () => {
+  assert.compareArray([,], []);
+}, 'Sparse arrays are not equivalent to empty arrays.');
+assert.throws(Test262Error, () => {
+  assert.compareArray([], [,]);
+}, 'Sparse arrays are not equivalent to empty arrays.');
diff --git a/test/harness/compare-array-symbol.js b/test/harness/compare-array-symbol.js
index bbcc8177f7..ca5369655f 100644
--- a/test/harness/compare-array-symbol.js
+++ b/test/harness/compare-array-symbol.js
@@ -11,7 +11,7 @@ features: [Symbol]
 var threw = false;
 
 try {
-	assert.compareArray([Symbol()], [Symbol('desc')]);
+  assert.compareArray([Symbol()], [Symbol('desc')]);
 } catch (err) {
   threw = true;