Testing sample (#500)

testing_app/test_driver/app.dart

@@ -0,0 +1,15 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_driver/driver_extension.dart';
+import 'package:testing_app/main.dart' as app;
+
+void main() {
+  // This line enables the extension.
+  enableFlutterDriverExtension();
+
+  // Call the `main()` function of the app, or call `runApp` with
+  // any widget you are interested in testing.
+  app.main();
+}