Add test for flexible_space_bar.0.dart (#157107)

Contributes to https://github.com/flutter/flutter/issues/130459

It adds a test for
- `examples/api/test/material/flexible_space_bar/flexible_space_bar.0_test.dart`

dev/bots/check_code_samples.dart

@@ -312,7 +312,6 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/material/selectable_region/selectable_region.0_test.dart',
   'examples/api/test/material/color_scheme/dynamic_content_color.0_test.dart',
   'examples/api/test/material/platform_menu_bar/platform_menu_bar.0_test.dart',
-  'examples/api/test/material/flexible_space_bar/flexible_space_bar.0_test.dart',
   'examples/api/test/material/navigation_rail/navigation_rail.extended_animation.0_test.dart',
   'examples/api/test/painting/star_border/star_border.0_test.dart',
   'examples/api/test/widgets/navigator/navigator.restorable_push_and_remove_until.0_test.dart',

examples/api/lib/material/flexible_space_bar/flexible_space_bar.0.dart

@@ -2,77 +2,83 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 
 /// Flutter code sample for [FlexibleSpaceBar].
 
-void main() => runApp(const MaterialApp(home: FlexibleSpaceBarExampleApp()));
+void main() => runApp(const FlexibleSpaceBarExampleApp());
 
 class FlexibleSpaceBarExampleApp extends StatelessWidget {
   const FlexibleSpaceBarExampleApp({super.key});
 
   @override
   Widget build(BuildContext context) {
-    return Scaffold(
+    return MaterialApp(
-      body: CustomScrollView(
+      scrollBehavior: const MaterialScrollBehavior().copyWith(
-        physics: const BouncingScrollPhysics(parent: AlwaysScrollableScrollPhysics()),
+        dragDevices: PointerDeviceKind.values.toSet(),
-        slivers: <Widget>[
+      ),
-          SliverAppBar(
+      home: Scaffold(
-            stretch: true,
+        body: CustomScrollView(
-            onStretchTrigger: () {
+          physics: const BouncingScrollPhysics(parent: AlwaysScrollableScrollPhysics()),
-              // Function callback for stretch
+          slivers: <Widget>[
-              return Future<void>.value();
+            SliverAppBar(
-            },
+              stretch: true,
-            expandedHeight: 300.0,
+              onStretchTrigger: () {
-            flexibleSpace: FlexibleSpaceBar(
+                // Function callback for stretch
-              stretchModes: const <StretchMode>[
+                return Future<void>.value();
-                StretchMode.zoomBackground,
+              },
-                StretchMode.blurBackground,
+              expandedHeight: 300.0,
-                StretchMode.fadeTitle,
+              flexibleSpace: FlexibleSpaceBar(
-              ],
+                stretchModes: const <StretchMode>[
-              centerTitle: true,
+                  StretchMode.zoomBackground,
-              title: const Text('Flight Report'),
+                  StretchMode.blurBackground,
-              background: Stack(
+                  StretchMode.fadeTitle,
-                fit: StackFit.expand,
+                ],
-                children: <Widget>[
+                centerTitle: true,
-                  Image.network(
+                title: const Text('Flight Report'),
-                    'https://flutter.github.io/assets-for-api-docs/assets/widgets/owl-2.jpg',
+                background: Stack(
-                    fit: BoxFit.cover,
+                  fit: StackFit.expand,
-                  ),
+                  children: <Widget>[
-                  const DecoratedBox(
+                    Image.network(
-                    decoration: BoxDecoration(
+                      'https://flutter.github.io/assets-for-api-docs/assets/widgets/owl-2.jpg',
-                      gradient: LinearGradient(
+                      fit: BoxFit.cover,
-                        begin: Alignment(0.0, 0.5),
+                    ),
-                        end: Alignment.center,
+                    const DecoratedBox(
-                        colors: <Color>[
+                      decoration: BoxDecoration(
-                          Color(0x60000000),
+                        gradient: LinearGradient(
-                          Color(0x00000000),
+                          begin: Alignment(0.0, 0.5),
-                        ],
+                          end: Alignment.center,
+                          colors: <Color>[
+                            Color(0x60000000),
+                            Color(0x00000000),
+                          ],
+                        ),
                       ),
                     ),
+                  ],
+                ),
+              ),
+            ),
+            SliverList(
+              delegate: SliverChildListDelegate(
+                const <Widget>[
+                  ListTile(
+                    leading: Icon(Icons.wb_sunny),
+                    title: Text('Sunday'),
+                    subtitle: Text('sunny, h: 80, l: 65'),
                   ),
+                  ListTile(
+                    leading: Icon(Icons.wb_sunny),
+                    title: Text('Monday'),
+                    subtitle: Text('sunny, h: 80, l: 65'),
+                  ),
+                  // ListTiles++
                 ],
               ),
             ),
-          ),
+          ],
-          SliverList(
+        ),
-            delegate: SliverChildListDelegate(
-              const <Widget>[
-                ListTile(
-                  leading: Icon(Icons.wb_sunny),
-                  title: Text('Sunday'),
-                  subtitle: Text('sunny, h: 80, l: 65'),
-                ),
-                ListTile(
-                  leading: Icon(Icons.wb_sunny),
-                  title: Text('Monday'),
-                  subtitle: Text('sunny, h: 80, l: 65'),
-                ),
-                // ListTiles++
-              ],
-            ),
-          ),
-        ],
       ),
     );
   }

examples/api/test/material/flexible_space_bar/flexible_space_bar.0_test.dart

@@ -0,0 +1,42 @@
+// 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_api_samples/material/flexible_space_bar/flexible_space_bar.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('The app bar stretches when over-scrolled', (WidgetTester tester) async {
+    await tester.pumpWidget(
+        const example.FlexibleSpaceBarExampleApp(),
+    );
+
+    expect(find.text('Flight Report'), findsOne);
+
+    expect(find.widgetWithText(ListTile, 'Sunday'), findsOne);
+    expect(find.widgetWithText(ListTile, 'Monday'), findsOne);
+    expect(find.text('sunny, h: 80, l: 65'), findsExactly(2));
+    expect(find.byIcon(Icons.wb_sunny), findsExactly(2));
+
+    final Finder appBarContainer = find.byType(Image);
+    final Size sizeBeforeScroll = tester.getSize(appBarContainer);
+    final Offset target = tester.getCenter(find.byType(ListTile).first);
+    final TestGesture gesture = await tester.startGesture(target);
+    await gesture.moveBy(const Offset(0.0, 100.0));
+    await tester.pump(const Duration(milliseconds: 10));
+    await gesture.up();
+    final Size sizeAfterScroll = tester.getSize(appBarContainer);
+
+    expect(sizeBeforeScroll.height, lessThan(sizeAfterScroll.height));
+    // Verifies ScrollBehavior.dragDevices is correctly set.
+  }, variant: TargetPlatformVariant.all());
+}