Update widget_test.dart

packages/css_colors/example/test/widget_test.dart

@@ -2,4 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-void main() {}
+import 'package:example/main.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Counter increments smoke test', (WidgetTester tester) async {
+    // Build our app and trigger a frame.
+    await tester.pumpWidget(const MyApp());
+  });
+}