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/orderBy.js

@@ -0,0 +1,43 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { falsey } from './utils.js';
+import orderBy from '../orderBy.js';
+
+describe('orderBy', function() {
+  var objects = [
+    { 'a': 'x', 'b': 3 },
+    { 'a': 'y', 'b': 4 },
+    { 'a': 'x', 'b': 1 },
+    { 'a': 'y', 'b': 2 }
+  ];
+
+  it('should sort by a single property by a specified order', function() {
+    var actual = orderBy(objects, 'a', 'desc');
+    assert.deepStrictEqual(actual, [objects[1], objects[3], objects[0], objects[2]]);
+  });
+
+  it('should sort by multiple properties by specified orders', function() {
+    var actual = orderBy(objects, ['a', 'b'], ['desc', 'asc']);
+    assert.deepStrictEqual(actual, [objects[3], objects[1], objects[2], objects[0]]);
+  });
+
+  it('should sort by a property in ascending order when its order is not specified', function() {
+    var expected = [objects[2], objects[0], objects[3], objects[1]],
+        actual = orderBy(objects, ['a', 'b']);
+
+    assert.deepStrictEqual(actual, expected);
+
+    expected = lodashStable.map(falsey, lodashStable.constant([objects[3], objects[1], objects[2], objects[0]]));
+
+    actual = lodashStable.map(falsey, function(order, index) {
+      return orderBy(objects, ['a', 'b'], index ? ['desc', order] : ['desc']);
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should work with `orders` specified as string objects', function() {
+    var actual = orderBy(objects, ['a'], [Object('desc')]);
+    assert.deepStrictEqual(actual, [objects[1], objects[3], objects[0], objects[2]]);
+  });
+});