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/runInContext.js

@@ -0,0 +1,29 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import runInContext from '../runInContext.js';
+import uniqueId from '../uniqueId.js';
+
+describe('runInContext', function() {
+  it('should not require a fully populated `context` object', function() {
+    var lodash = runInContext({
+      'setTimeout': function(func) { func(); }
+    });
+
+    var pass = false;
+    lodash.delay(function() { pass = true; }, 32);
+    assert.ok(pass);
+  });
+
+  it('should use a zeroed `_.uniqueId` counter', function() {
+    lodashStable.times(2, uniqueId);
+
+    var oldId = Number(uniqueId()),
+        lodash = runInContext();
+
+    assert.ok(uniqueId() > oldId);
+
+    var id = lodash.uniqueId();
+    assert.strictEqual(id, '1');
+    assert.ok(id < oldId);
+  });
+});