Improve coverage for section 21: String (#712)

This changeset increases coverage for section 21, specifically "21.1 String
Objects".

* Add tests for "this" validation of String methods

* Add tests for ToNumber as used by String methods

* Add test for `length` prop of exotic String objs

* fixup! Add test for `length` prop of exotic String objs

test/built-ins/String/length.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-properties-of-string-instances-length
+es6id: 21.1.4.1
+description: The "length" property of String objects
+info: |
+  [...]
+  4. Return ? StringCreate(s, ? GetPrototypeFromConstructor(NewTarget,
+     "%StringPrototype%")).
+includes: [propertyHelper.js]
+---*/
+
+var str = new String('');
+
+verifyNotEnumerable(str, 'length');
+verifyNotWritable(str, 'length');
+verifyNotConfigurable(str, 'length');
+
+assert.sameValue(str.length, 0, 'empty string');
+
+str = new String(' ');
+assert.sameValue(str.length, 1, 'whitespace');
+
+str = new String(' \b ');
+assert.sameValue(str.length, 3, 'character escape (U+008, "backspace")');
+
+str = new String('\ud834\udf06');
+assert.sameValue(str.length, 2,  'Unicode escape (surrogate pair)');

test/built-ins/String/prototype/charAt/pos-coerce-err.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.charat
+es6id: 21.1.3.1
+description: Error when attempting to coerce providec "pos" to a Number
+info: |
+  [...]
+  3. Let position be ? ToInteger(pos).
+  [...]
+
+  7.1.4 ToInteger
+
+  1. Let number be ? ToNumber(argument).
+---*/
+
+var noCoerce = Object.create(null);
+
+assert.throws(TypeError, function() {
+  ''.charAt(noCoerce);
+});

test/built-ins/String/prototype/charAt/pos-coerce-string.js

@@ -0,0 +1,17 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.charat
+es6id: 21.1.3.1
+description: Coercion of "pos" string value into number
+info: |
+  [...]
+  3. Let position be ? ToInteger(pos).
+  [...]
+
+  7.1.4 ToInteger
+
+  1. Let number be ? ToNumber(argument).
+---*/
+
+assert.sameValue('abcd'.charAt('   +00200.0000E-0002   '), 'c');

test/built-ins/String/prototype/charAt/pos-rounding.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.charat
+es6id: 21.1.3.1
+description: Rounding of the provided "pos" number
+info: |
+  [...]
+  3. Let position be ? ToInteger(pos).
+  [...]
+
+  7.1.4 ToInteger
+
+  1. Let number be ? ToNumber(argument).
+  2. If number is NaN, return +0.
+  3. If number is +0, -0, +∞, or -∞, return number.
+  4. Return the number value that is the same sign as number and whose
+     magnitude is floor(abs(number)). 
+---*/
+
+assert.sameValue('abc'.charAt(-0.99999), 'a', '-0.99999');
+assert.sameValue('abc'.charAt(-0.00001), 'a', '-0.00001');
+assert.sameValue('abc'.charAt(0.00001), 'a', '0.00001');
+assert.sameValue('abc'.charAt(0.99999), 'a', '0.99999');
+assert.sameValue('abc'.charAt(1.00001), 'b', '1.00001');
+assert.sameValue('abc'.charAt(1.99999), 'b', '1.99999');

test/built-ins/String/prototype/charAt/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.charat
+es6id: 21.1.3.1
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var charAt = String.prototype.charAt;
+
+assert.sameValue(typeof charAt, 'function');
+
+assert.throws(TypeError, function() {
+  charAt.call(undefined, 0);
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  charAt.call(null, 0);
+}, 'null');

test/built-ins/String/prototype/charCodeAt/pos-coerce-err.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.charcodeat
+es6id: 21.1.3.2
+description: Error when attempting to coerce providec "pos" to a Number
+info: |
+  [...]
+  3. Let position be ? ToInteger(pos).
+  [...]
+
+  7.1.4 ToInteger
+
+  1. Let number be ? ToNumber(argument).
+---*/
+
+var noCoerce = Object.create(null);
+
+assert.throws(TypeError, function() {
+  ''.charCodeAt(noCoerce);
+});

test/built-ins/String/prototype/charCodeAt/pos-coerce-string.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.charcodeat
+es6id: 21.1.3.2
+description: Coercion of "pos" string value into number
+info: |
+  [...]
+  3. Let position be ? ToInteger(pos).
+  [...]
+
+  7.1.4 ToInteger
+
+  1. Let number be ? ToNumber(argument).
+---*/
+
+var cCode = 99;
+
+assert.sameValue('abcd'.charCodeAt('   +00200.0000E-0002   '), cCode);

test/built-ins/String/prototype/charCodeAt/pos-rounding.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.charcodeat
+es6id: 21.1.3.2
+description: Rounding of the provided "pos" number
+info: |
+  [...]
+  3. Let position be ? ToInteger(pos).
+  [...]
+
+  7.1.4 ToInteger
+
+  1. Let number be ? ToNumber(argument).
+  2. If number is NaN, return +0.
+  3. If number is +0, -0, +∞, or -∞, return number.
+  4. Return the number value that is the same sign as number and whose
+     magnitude is floor(abs(number)). 
+---*/
+
+var aCode = 97;
+var bCode = 98;
+
+assert.sameValue('abc'.charCodeAt(-0.99999), aCode, '-0.99999');
+assert.sameValue('abc'.charCodeAt(-0.00001), aCode, '-0.00001');
+assert.sameValue('abc'.charCodeAt(0.00001), aCode, '0.00001');
+assert.sameValue('abc'.charCodeAt(0.99999), aCode, '0.99999');
+assert.sameValue('abc'.charCodeAt(1.00001), bCode, '1.00001');
+assert.sameValue('abc'.charCodeAt(1.99999), bCode, '1.99999');

test/built-ins/String/prototype/charCodeAt/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.charcodeat
+es6id: 21.1.3.2
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var charCodeAt = String.prototype.charCodeAt;
+
+assert.sameValue(typeof charCodeAt, 'function');
+
+assert.throws(TypeError, function() {
+  charCodeAt.call(undefined, 0);
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  charCodeAt.call(null, 0);
+}, 'null');

test/built-ins/String/prototype/concat/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.concat
+es6id: 21.1.3.4
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var concat = String.prototype.concat;
+
+assert.sameValue(typeof concat, 'function');
+
+assert.throws(TypeError, function() {
+  concat.call(undefined, '');
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  concat.call(null, '');
+}, 'null');

test/built-ins/String/prototype/indexOf/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.indexof
+es6id: 21.1.3.8
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var indexOf = String.prototype.indexOf;
+
+assert.sameValue(typeof indexOf, 'function');
+
+assert.throws(TypeError, function() {
+  indexOf.call(undefined, '');
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  indexOf.call(null, '');
+}, 'null');

test/built-ins/String/prototype/lastIndexOf/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.lastindexof
+es6id: 21.1.3.9
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var lastIndexOf = String.prototype.lastIndexOf;
+
+assert.sameValue(typeof lastIndexOf, 'function');
+
+assert.throws(TypeError, function() {
+  lastIndexOf.call(undefined, '');
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  lastIndexOf.call(null, '');
+}, 'null');

test/built-ins/String/prototype/localeCompare/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.localecompare
+es6id: 21.1.3.10
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var localeCompare = String.prototype.localeCompare;
+
+assert.sameValue(typeof localeCompare, 'function');
+
+assert.throws(TypeError, function() {
+  localeCompare.call(undefined, '');
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  localeCompare.call(null, '');
+}, 'null');

test/built-ins/String/prototype/match/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.match
+es6id: 21.1.3.11
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var match = String.prototype.match;
+
+assert.sameValue(typeof match, 'function');
+
+assert.throws(TypeError, function() {
+  match.call(undefined, /./);
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  match.call(null, /./);
+}, 'null');

test/built-ins/String/prototype/replace/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.replace
+es6id: 21.1.3.14
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var replace = String.prototype.replace;
+
+assert.sameValue(typeof replace, 'function');
+
+assert.throws(TypeError, function() {
+  replace.call(undefined, '', '');
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  replace.call(null, '', '');
+}, 'null');

test/built-ins/String/prototype/search/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.search
+es6id: 21.1.3.15
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var search = String.prototype.search;
+
+assert.sameValue(typeof search, 'function');
+
+assert.throws(TypeError, function() {
+  search.call(undefined, /./);
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  search.call(null, /./);
+}, 'null');

test/built-ins/String/prototype/slice/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.slice
+es6id: 21.1.3.16
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var slice = String.prototype.slice;
+
+assert.sameValue(typeof slice, 'function');
+
+assert.throws(TypeError, function() {
+  slice.call(undefined, 0);
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  slice.call(null, 0);
+}, 'null');

test/built-ins/String/prototype/split/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.split
+es6id: 21.1.3.17
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var split = String.prototype.split;
+
+assert.sameValue(typeof split, 'function');
+
+assert.throws(TypeError, function() {
+  split.call(undefined, '');
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  split.call(null, '');
+}, 'null');

test/built-ins/String/prototype/substring/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.substring
+es6id: 21.1.3.19
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var substring = String.prototype.substring;
+
+assert.sameValue(typeof substring, 'function');
+
+assert.throws(TypeError, function() {
+  substring.call(undefined, 0, 1);
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  substring.call(null, 0, 1);
+}, 'null');

test/built-ins/String/prototype/toLocaleLowerCase/this-value-not-obj-coercible.js

@@ -0,0 +1,27 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.tolocalelowercase
+es6id: 21.1.3.20
+description: The "this" value must be object-coercible
+info: |
+  This function works exactly the same as toLowerCase except that its result is
+  intended to yield the correct result for the host environment's current
+  locale, rather than a locale-independent result.
+
+  21.1.3.24 String.prototype.toLowerCase
+
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var toLocaleLowerCase = String.prototype.toLocaleLowerCase;
+
+assert.sameValue(typeof toLocaleLowerCase, 'function');
+
+assert.throws(TypeError, function() {
+  toLocaleLowerCase.call(undefined);
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  toLocaleLowerCase.call(null);
+}, 'null');

test/built-ins/String/prototype/toLocaleUpperCase/this-value-not-obj-coercible.js

@@ -0,0 +1,33 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.tolocaleuppercase
+es6id: 21.1.3.21
+description: The "this" value must be object-coercible
+info: |
+  This function works exactly the same as toUpperCase except that its result is
+  intended to yield the correct result for the host environment's current
+  locale, rather than a locale-independent result.
+
+  21.1.3.26 String.prototype.toUpperCase
+
+  This function behaves in exactly the same way as
+  String.prototype.toLowerCase, except that code points are mapped to their
+  uppercase equivalents as specified in the Unicode Character Database.
+
+  21.1.3.24 String.prototype.toLowerCase
+
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var toLocaleUpperCase = String.prototype.toLocaleUpperCase;
+
+assert.sameValue(typeof toLocaleUpperCase, 'function');
+
+assert.throws(TypeError, function() {
+  toLocaleUpperCase.call(undefined);
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  toLocaleUpperCase.call(null);
+}, 'null');

test/built-ins/String/prototype/toLowerCase/this-value-not-obj-coercible.js

@@ -0,0 +1,21 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.tolowercase
+es6id: 21.1.3.22
+description: The "this" value must be object-coercible
+info: |
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var toLowerCase = String.prototype.toLowerCase;
+
+assert.sameValue(typeof toLowerCase, 'function');
+
+assert.throws(TypeError, function() {
+  toLowerCase.call(undefined);
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  toLowerCase.call(null);
+}, 'null');

test/built-ins/String/prototype/toUpperCase/this-value-not-obj-coercible.js

@@ -0,0 +1,27 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.touppercase
+es6id: 21.1.3.24
+description: The "this" value must be object-coercible
+info: |
+  This function behaves in exactly the same way as
+  String.prototype.toLowerCase, except that code points are mapped to their
+  uppercase equivalents as specified in the Unicode Character Database.
+
+  21.1.3.24 String.prototype.toLowerCase
+
+  1. Let O be ? RequireObjectCoercible(this value).
+---*/
+
+var toUpperCase = String.prototype.toUpperCase;
+
+assert.sameValue(typeof toUpperCase, 'function');
+
+assert.throws(TypeError, function() {
+  toUpperCase.call(undefined);
+}, 'undefined');
+
+assert.throws(TypeError, function() {
+  toUpperCase.call(null);
+}, 'null');