Add tests for gesture_detector.0.dart and gesture_detector.1.dart API examples. (#146724)

This PR contributes to flutter/flutter#130459

### Description
- Adds `examples/api/test/widgets/gesture_detector/gesture_detector.0_test.dart` test
- Adds `examples/api/test/widgets/gesture_detector/gesture_detector.1_test.dart` test

Author: ksokolovskyi

dev/bots/check_code_samples.dart

@@ -453,8 +453,6 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/widgets/interactive_viewer/interactive_viewer.transformation_controller.0_test.dart',
   'examples/api/test/widgets/interactive_viewer/interactive_viewer.0_test.dart',
   'examples/api/test/widgets/notification_listener/notification.0_test.dart',
-  'examples/api/test/widgets/gesture_detector/gesture_detector.1_test.dart',
-  'examples/api/test/widgets/gesture_detector/gesture_detector.0_test.dart',
   'examples/api/test/widgets/editable_text/text_editing_controller.0_test.dart',
   'examples/api/test/widgets/editable_text/editable_text.on_changed.0_test.dart',
   'examples/api/test/widgets/undo_history/undo_history_controller.0_test.dart',

examples/api/test/widgets/gesture_detector/gesture_detector.0_test.dart

@@ -0,0 +1,40 @@
+// Copyright 2014 The Flutter Authors. 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/material.dart';
+import 'package:flutter_api_samples/widgets/gesture_detector/gesture_detector.0.dart'
+    as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets(
+    'GestureDetector updates icon color and text on tap',
+    (WidgetTester tester) async {
+      await tester.pumpWidget(
+        const example.GestureDetectorExampleApp(),
+      );
+
+      Icon icon = tester.widget(find.byIcon(Icons.lightbulb_outline));
+
+      expect(find.text('TURN LIGHT ON'), findsOneWidget);
+      expect(icon.color, Colors.black);
+
+      await tester.tap(find.byType(GestureDetector));
+      await tester.pump();
+
+      icon = tester.widget(find.byIcon(Icons.lightbulb_outline));
+
+      expect(find.text('TURN LIGHT OFF'), findsOneWidget);
+      expect(icon.color, Colors.yellow.shade600);
+
+      await tester.tap(find.byType(GestureDetector));
+      await tester.pump();
+
+      icon = tester.widget(find.byIcon(Icons.lightbulb_outline));
+
+      expect(find.text('TURN LIGHT ON'), findsOneWidget);
+      expect(icon.color, Colors.black);
+    },
+  );
+}

examples/api/test/widgets/gesture_detector/gesture_detector.1_test.dart

@@ -0,0 +1,52 @@
+// Copyright 2014 The Flutter Authors. 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/material.dart';
+import 'package:flutter_api_samples/widgets/gesture_detector/gesture_detector.1.dart'
+    as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets(
+    'GestureDetector updates Container color on tap',
+    (WidgetTester tester) async {
+      await tester.pumpWidget(
+        const example.GestureDetectorExampleApp(),
+      );
+
+      Container container = tester.widget(
+        find.ancestor(
+          of: find.byType(GestureDetector),
+          matching: find.byType(Container),
+        ),
+      );
+
+      expect(container.color, Colors.white);
+
+      await tester.tap(find.byType(GestureDetector));
+      await tester.pump();
+
+      container = tester.widget(
+        find.ancestor(
+          of: find.byType(GestureDetector),
+          matching: find.byType(Container),
+        ),
+      );
+
+      expect(container.color, Colors.yellow);
+
+      await tester.tap(find.byType(GestureDetector));
+      await tester.pump();
+
+      container = tester.widget(
+        find.ancestor(
+          of: find.byType(GestureDetector),
+          matching: find.byType(Container),
+        ),
+      );
+
+      expect(container.color, Colors.white);
+    },
+  );
+}