Add tests for color_filtered.0.dart example. (#151064)

This PR contributes to https://github.com/flutter/flutter/issues/130459

### Description
- Adds tests for `examples/api/lib/widgets/color_filter/color_filtered.0.dart`

dev/bots/check_code_samples.dart

@@ -380,7 +380,6 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/widgets/restoration/restoration_mixin.0_test.dart',
   'examples/api/test/widgets/actions/action_listener.0_test.dart',
   'examples/api/test/widgets/actions/focusable_action_detector.0_test.dart',
-  'examples/api/test/widgets/color_filter/color_filtered.0_test.dart',
   'examples/api/test/widgets/focus_scope/focus_scope.0_test.dart',
   'examples/api/test/widgets/scroll_view/custom_scroll_view.1_test.dart',
   'examples/api/test/animation/curves/curve2_d.0_test.dart',

examples/api/test/widgets/color_filter/color_filtered.0_test.dart

@@ -0,0 +1,53 @@
+// 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 'dart:io';
+
+import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter_api_samples/widgets/color_filter/color_filtered.0.dart'
+    as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  // The app being tested loads images via HTTP which the test
+  // framework defeats by default.
+  setUpAll(() {
+    HttpOverrides.global = null;
+  });
+
+  testWidgets('Color filters are applied to the images', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.ColorFilteredExampleApp(),
+    );
+
+    await tester.pumpAndSettle();
+
+    // Verify that two images are displayed.
+    expect(find.byType(Image), findsNWidgets(2));
+
+    RenderObject renderObject = tester.firstRenderObject(
+      find.byType(ColorFiltered).first,
+    );
+    ColorFilterLayer colorFilterLayer =
+        renderObject.debugLayer! as ColorFilterLayer;
+
+    // Verify that red colored filter with modulate blend mode is applied to the first image.
+    expect(
+      colorFilterLayer.colorFilter,
+      equals(const ColorFilter.mode(Colors.red, BlendMode.modulate)),
+    );
+
+    renderObject = tester.firstRenderObject(
+      find.byType(ColorFiltered).last,
+    );
+    colorFilterLayer = renderObject.debugLayer! as ColorFilterLayer;
+
+    // Verify that grey colored filter with saturation blend mode is applied to the first image.
+    expect(
+      colorFilterLayer.colorFilter,
+      equals(const ColorFilter.mode(Colors.grey, BlendMode.saturation)),
+    );
+  });
+}