Add test for nested_scroll_view_state.0.dart (#157714)

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

It adds a test for
- `examples/api/lib/widgets/nested_scroll_view/nested_scroll_view_state.0.dart`

dev/bots/check_code_samples.dart

@@ -310,7 +310,6 @@ class SampleChecker {
 // See https://github.com/flutter/flutter/issues/130459
 final Set<String> _knownMissingTests = <String>{
   'examples/api/test/material/color_scheme/dynamic_content_color.0_test.dart',
-  'examples/api/test/widgets/nested_scroll_view/nested_scroll_view_state.0_test.dart',
   'examples/api/test/widgets/scroll_position/scroll_metrics_notification.0_test.dart',
   'examples/api/test/widgets/media_query/media_query_data.system_gesture_insets.0_test.dart',
   'examples/api/test/widgets/image/image.frame_builder.0_test.dart',

examples/api/lib/widgets/nested_scroll_view/nested_scroll_view_state.0.dart

@@ -24,7 +24,6 @@ final GlobalKey<NestedScrollViewState> globalKey = GlobalKey();
 class NestedScrollViewStateExample extends StatelessWidget {
   const NestedScrollViewStateExample({super.key});
 
-  @override
   @override
   Widget build(BuildContext context) {
     return NestedScrollView(
@@ -42,6 +41,10 @@ class NestedScrollViewStateExample extends StatelessWidget {
     );
   }
 
+  ScrollController get outerController {
+    return globalKey.currentState!.outerController;
+  }
+
   ScrollController get innerController {
     return globalKey.currentState!.innerController;
   }

examples/api/test/widgets/nested_scroll_view/nested_scroll_view_state.0_test.dart

@@ -0,0 +1,38 @@
+// 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/gestures.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/widgets/nested_scroll_view/nested_scroll_view_state.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Access the outer and inner controllers', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.NestedScrollViewStateExampleApp(),
+    );
+
+    expect(find.byType(NestedScrollView), findsOne);
+    expect(find.widgetWithText(SliverAppBar, 'NestedScrollViewState Demo!'), findsOne);
+    expect(find.byType(CustomScrollView), findsOne);
+
+    final example.NestedScrollViewStateExample widget = tester.widget<example.NestedScrollViewStateExample>(
+      find.byType(example.NestedScrollViewStateExample),
+    );
+
+    final ScrollController outerController = widget.outerController;
+    final ScrollController innerController = widget.innerController;
+
+    expect(outerController.offset, 0);
+    expect(innerController.offset, 0);
+
+    await tester.sendEventToBinding(const PointerScrollEvent(scrollDelta: Offset(0.0, 10.0)));
+    await tester.pump();
+
+    await tester.pumpAndSettle();
+
+    expect(outerController.offset, 10);
+    expect(innerController.offset, 0);
+  });
+}