Add initial test files from lodash v4. (#4172)

* Install test dependencies.

* Add initial test files.

These files were created using a simplistic AST manipulator using `recast` to
preserve formatting. There's bound to be a huge chunk of errors, but this serves
as a good start. QUnit was replaced with Mocha, with ES2015 imports running via
`esm`.

As far as possible, QUnit-specific syntax has been replaced with Mocha's
`describe` and `it`, while the native Node.js `assert` module is used for
assertions. Files in the `test` directory ending in `.test.js` will be treated
as test files.

* Add initial passing files to test run.

test/words.js

@@ -0,0 +1,123 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { burredLetters, _, stubArray } from './utils.js';
+
+describe('words', function() {
+  it('should match words containing Latin Unicode letters', function() {
+    var expected = lodashStable.map(burredLetters, function(letter) {
+      return [letter];
+    });
+
+    var actual = lodashStable.map(burredLetters, function(letter) {
+      return _.words(letter);
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should support a `pattern`', function() {
+    assert.deepStrictEqual(_.words('abcd', /ab|cd/g), ['ab', 'cd']);
+    assert.deepStrictEqual(_.words('abcd', 'ab|cd'), ['ab']);
+  });
+
+  it('should work with compound words', function() {
+    assert.deepStrictEqual(_.words('12ft'), ['12', 'ft']);
+    assert.deepStrictEqual(_.words('aeiouAreVowels'), ['aeiou', 'Are', 'Vowels']);
+    assert.deepStrictEqual(_.words('enable 6h format'), ['enable', '6', 'h', 'format']);
+    assert.deepStrictEqual(_.words('enable 24H format'), ['enable', '24', 'H', 'format']);
+    assert.deepStrictEqual(_.words('isISO8601'), ['is', 'ISO', '8601']);
+    assert.deepStrictEqual(_.words('LETTERSAeiouAreVowels'), ['LETTERS', 'Aeiou', 'Are', 'Vowels']);
+    assert.deepStrictEqual(_.words('tooLegit2Quit'), ['too', 'Legit', '2', 'Quit']);
+    assert.deepStrictEqual(_.words('walk500Miles'), ['walk', '500', 'Miles']);
+    assert.deepStrictEqual(_.words('xhr2Request'), ['xhr', '2', 'Request']);
+    assert.deepStrictEqual(_.words('XMLHttp'), ['XML', 'Http']);
+    assert.deepStrictEqual(_.words('XmlHTTP'), ['Xml', 'HTTP']);
+    assert.deepStrictEqual(_.words('XmlHttp'), ['Xml', 'Http']);
+  });
+
+  it('should work with compound words containing diacritical marks', function() {
+    assert.deepStrictEqual(_.words('LETTERSÆiouAreVowels'), ['LETTERS', 'Æiou', 'Are', 'Vowels']);
+    assert.deepStrictEqual(_.words('æiouAreVowels'), ['æiou', 'Are', 'Vowels']);
+    assert.deepStrictEqual(_.words('æiou2Consonants'), ['æiou', '2', 'Consonants']);
+  });
+
+  it('should not treat contractions as separate words', function() {
+    var postfixes = ['d', 'll', 'm', 're', 's', 't', 've'];
+
+    lodashStable.each(["'", '\u2019'], function(apos) {
+      lodashStable.times(2, function(index) {
+        var actual = lodashStable.map(postfixes, function(postfix) {
+          var string = 'a b' + apos + postfix +  ' c';
+          return _.words(string[index ? 'toUpperCase' : 'toLowerCase']());
+        });
+
+        var expected = lodashStable.map(postfixes, function(postfix) {
+          var words = ['a', 'b' + apos + postfix, 'c'];
+          return lodashStable.map(words, function(word) {
+            return word[index ? 'toUpperCase' : 'toLowerCase']();
+          });
+        });
+
+        assert.deepStrictEqual(actual, expected);
+      });
+    });
+  });
+
+  it('should not treat ordinal numbers as separate words', function() {
+    var ordinals = ['1st', '2nd', '3rd', '4th'];
+
+    lodashStable.times(2, function(index) {
+      var expected = lodashStable.map(ordinals, function(ordinal) {
+        return [ordinal[index ? 'toUpperCase' : 'toLowerCase']()];
+      });
+
+      var actual = lodashStable.map(expected, function(words) {
+        return _.words(words[0]);
+      });
+
+      assert.deepStrictEqual(actual, expected);
+    });
+  });
+
+  it('should not treat mathematical operators as words', function() {
+    var operators = ['\xac', '\xb1', '\xd7', '\xf7'],
+        expected = lodashStable.map(operators, stubArray),
+        actual = lodashStable.map(operators, _.words);
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should not treat punctuation as words', function() {
+    var marks = [
+      '\u2012', '\u2013', '\u2014', '\u2015',
+      '\u2024', '\u2025', '\u2026',
+      '\u205d', '\u205e'
+    ];
+
+    var expected = lodashStable.map(marks, stubArray),
+        actual = lodashStable.map(marks, _.words);
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should work as an iteratee for methods like `_.map`', function() {
+    var strings = lodashStable.map(['a', 'b', 'c'], Object),
+        actual = lodashStable.map(strings, _.words);
+
+    assert.deepStrictEqual(actual, [['a'], ['b'], ['c']]);
+  });
+
+  it('should prevent ReDoS', function() {
+    var largeWordLen = 50000,
+        largeWord = 'A'.repeat(largeWordLen),
+        maxMs = 1000,
+        startTime = lodashStable.now();
+
+    assert.deepStrictEqual(_.words(largeWord + 'ÆiouAreVowels'), [largeWord, 'Æiou', 'Are', 'Vowels']);
+
+    var endTime = lodashStable.now(),
+        timeSpent = endTime - startTime;
+
+    assert.ok(timeSpent < maxMs, 'operation took ' + timeSpent + 'ms');
+  });
+});