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/uniq-methods.js

@@ -0,0 +1,123 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { _, LARGE_ARRAY_SIZE, isEven } from './utils.js';
+import sortBy from '../sortBy.js';
+
+describe('uniq methods', function() {
+  lodashStable.each(['uniq', 'uniqBy', 'uniqWith', 'sortedUniq', 'sortedUniqBy'], function(methodName) {
+    var func = _[methodName],
+        isSorted = /^sorted/.test(methodName),
+        objects = [{ 'a': 2 }, { 'a': 3 }, { 'a': 1 }, { 'a': 2 }, { 'a': 3 }, { 'a': 1 }];
+
+    if (isSorted) {
+      objects = sortBy(objects, 'a');
+    }
+    else {
+      it('`_.' + methodName + '` should return unique values of an unsorted array', function() {
+        var array = [2, 1, 2];
+        assert.deepStrictEqual(func(array), [2, 1]);
+      });
+    }
+    it('`_.' + methodName + '` should return unique values of a sorted array', function() {
+      var array = [1, 2, 2];
+      assert.deepStrictEqual(func(array), [1, 2]);
+    });
+
+    it('`_.' + methodName + '` should treat object instances as unique', function() {
+      assert.deepStrictEqual(func(objects), objects);
+    });
+
+    it('`_.' + methodName + '` should treat `-0` as `0`', function() {
+      var actual = lodashStable.map(func([-0, 0]), lodashStable.toString);
+      assert.deepStrictEqual(actual, ['0']);
+    });
+
+    it('`_.' + methodName + '` should match `NaN`', function() {
+      assert.deepStrictEqual(func([NaN, NaN]), [NaN]);
+    });
+
+    it('`_.' + methodName + '` should work with large arrays', function() {
+      var largeArray = [],
+          expected = [0, {}, 'a'],
+          count = Math.ceil(LARGE_ARRAY_SIZE / expected.length);
+
+      lodashStable.each(expected, function(value) {
+        lodashStable.times(count, function() {
+          largeArray.push(value);
+        });
+      });
+
+      assert.deepStrictEqual(func(largeArray), expected);
+    });
+
+    it('`_.' + methodName + '` should work with large arrays of `-0` as `0`', function() {
+      var largeArray = lodashStable.times(LARGE_ARRAY_SIZE, function(index) {
+        return isEven(index) ? -0 : 0;
+      });
+
+      var actual = lodashStable.map(func(largeArray), lodashStable.toString);
+      assert.deepStrictEqual(actual, ['0']);
+    });
+
+    it('`_.' + methodName + '` should work with large arrays of boolean, `NaN`, and nullish values', function() {
+      var largeArray = [],
+          expected = [null, undefined, false, true, NaN],
+          count = Math.ceil(LARGE_ARRAY_SIZE / expected.length);
+
+      lodashStable.each(expected, function(value) {
+        lodashStable.times(count, function() {
+          largeArray.push(value);
+        });
+      });
+
+      assert.deepStrictEqual(func(largeArray), expected);
+    });
+
+    it('`_.' + methodName + '` should work with large arrays of symbols', function() {
+      if (Symbol) {
+        var largeArray = lodashStable.times(LARGE_ARRAY_SIZE, Symbol);
+        assert.deepStrictEqual(func(largeArray), largeArray);
+      }
+    });
+
+    it('`_.' + methodName + '` should work with large arrays of well-known symbols', function() {
+      // See http://www.ecma-international.org/ecma-262/6.0/#sec-well-known-symbols.
+      if (Symbol) {
+        var expected = [
+          Symbol.hasInstance, Symbol.isConcatSpreadable, Symbol.iterator,
+          Symbol.match, Symbol.replace, Symbol.search, Symbol.species,
+          Symbol.split, Symbol.toPrimitive, Symbol.toStringTag, Symbol.unscopables
+        ];
+
+        var largeArray = [],
+            count = Math.ceil(LARGE_ARRAY_SIZE / expected.length);
+
+        expected = lodashStable.map(expected, function(symbol) {
+          return symbol || {};
+        });
+
+        lodashStable.each(expected, function(value) {
+          lodashStable.times(count, function() {
+            largeArray.push(value);
+          });
+        });
+
+        assert.deepStrictEqual(func(largeArray), expected);
+      }
+    });
+
+    it('`_.' + methodName + '` should distinguish between numbers and numeric strings', function() {
+      var largeArray = [],
+          expected = ['2', 2, Object('2'), Object(2)],
+          count = Math.ceil(LARGE_ARRAY_SIZE / expected.length);
+
+      lodashStable.each(expected, function(value) {
+        lodashStable.times(count, function() {
+          largeArray.push(value);
+        });
+      });
+
+      assert.deepStrictEqual(func(largeArray), expected);
+    });
+  });
+});