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/lodash(...).commit.js

@@ -0,0 +1,21 @@
+import assert from 'assert';
+
+describe('lodash(...).commit', function() {
+  it('should execute the chained sequence and returns the wrapped result', function() {
+    var array = [1],
+        wrapped = _(array).push(2).push(3);
+
+    assert.deepEqual(array, [1]);
+
+    var otherWrapper = wrapped.commit();
+    assert.ok(otherWrapper instanceof _);
+    assert.deepEqual(otherWrapper.value(), [1, 2, 3]);
+    assert.deepEqual(wrapped.value(), [1, 2, 3, 2, 3]);
+  });
+
+  it('should track the `__chain__` value of a wrapper', function() {
+    var wrapped = _([1]).chain().commit().head();
+    assert.ok(wrapped instanceof _);
+    assert.strictEqual(wrapped.value(), 1);
+  });
+});