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/chunk.js

@@ -0,0 +1,50 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { falsey, stubArray } from './utils.js';
+import chunk from '../chunk.js';
+
+describe('chunk', function() {
+  var array = [0, 1, 2, 3, 4, 5];
+
+  it('should return chunked arrays', function() {
+    var actual = chunk(array, 3);
+    assert.deepStrictEqual(actual, [[0, 1, 2], [3, 4, 5]]);
+  });
+
+  it('should return the last chunk as remaining elements', function() {
+    var actual = chunk(array, 4);
+    assert.deepStrictEqual(actual, [[0, 1, 2, 3], [4, 5]]);
+  });
+
+  it('should treat falsey `size` values, except `undefined`, as `0`', function() {
+    var expected = lodashStable.map(falsey, function(value) {
+      return value === undefined ? [[0], [1], [2], [3], [4], [5]] : [];
+    });
+
+    var actual = lodashStable.map(falsey, function(size, index) {
+      return index ? chunk(array, size) : chunk(array);
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should ensure the minimum `size` is `0`', function() {
+    var values = lodashStable.reject(falsey, lodashStable.isUndefined).concat(-1, -Infinity),
+        expected = lodashStable.map(values, stubArray);
+
+    var actual = lodashStable.map(values, function(n) {
+      return chunk(array, n);
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should coerce `size` to an integer', function() {
+    assert.deepStrictEqual(chunk(array, array.length / 4), [[0], [1], [2], [3], [4], [5]]);
+  });
+
+  it('should work as an iteratee for methods like `_.map`', function() {
+    var actual = lodashStable.map([[1, 2], [3, 4]], chunk);
+    assert.deepStrictEqual(actual, [[[1], [2]], [[3], [4]]]);
+  });
+});