Add a dummy test to make CI pass.

packages/rules-unit-testing/test/dummy.test.ts

@@ -0,0 +1,23 @@
+/**
+ * @license
+ * Copyright 2019 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { expect } from 'chai';
+
+// TODO: Real tests (coming in the following PRs).
+it('true should equal to true', () => {
+  expect(true).to.be.true;
+});