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/sampleSize.js

@@ -0,0 +1,76 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { falsey, empties, stubArray } from './utils.js';
+import sampleSize from '../sampleSize.js';
+
+describe('sampleSize', function() {
+  var array = [1, 2, 3];
+
+  it('should return an array of random elements', function() {
+    var actual = sampleSize(array, 2);
+
+    assert.strictEqual(actual.length, 2);
+    assert.deepStrictEqual(lodashStable.difference(actual, array), []);
+  });
+
+  it('should contain elements of the collection', function() {
+    var actual = sampleSize(array, array.length).sort();
+
+    assert.deepStrictEqual(actual, array);
+  });
+
+  it('should treat falsey `size` values, except `undefined`, as `0`', function() {
+    var expected = lodashStable.map(falsey, function(value) {
+      return value === undefined ? ['a'] : [];
+    });
+
+    var actual = lodashStable.map(falsey, function(size, index) {
+      return index ? sampleSize(['a'], size) : sampleSize(['a']);
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should return an empty array when `n` < `1` or `NaN`', function() {
+    lodashStable.each([0, -1, -Infinity], function(n) {
+      assert.deepStrictEqual(sampleSize(array, n), []);
+    });
+  });
+
+  it('should return all elements when `n` >= `length`', function() {
+    lodashStable.each([3, 4, Math.pow(2, 32), Infinity], function(n) {
+      var actual = sampleSize(array, n).sort();
+      assert.deepStrictEqual(actual, array);
+    });
+  });
+
+  it('should coerce `n` to an integer', function() {
+    var actual = sampleSize(array, 1.6);
+    assert.strictEqual(actual.length, 1);
+  });
+
+  it('should return an empty array for empty collections', function() {
+    var expected = lodashStable.map(empties, stubArray);
+
+    var actual = lodashStable.transform(empties, function(result, value) {
+      try {
+        result.push(sampleSize(value, 1));
+      } catch (e) {}
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should sample an object', function() {
+    var object = { 'a': 1, 'b': 2, 'c': 3 },
+        actual = sampleSize(object, 2);
+
+    assert.strictEqual(actual.length, 2);
+    assert.deepStrictEqual(lodashStable.difference(actual, lodashStable.values(object)), []);
+  });
+
+  it('should work as an iteratee for methods like `_.map`', function() {
+    var actual = lodashStable.map([['a']], sampleSize);
+    assert.deepStrictEqual(actual, [['a']]);
+  });
+});