Add test for error_widget.0_test.dart (#153103)

Add test for error_widget.0_test.dart which is listed in this issue 

related to this issue https://github.com/flutter/flutter/issues/130459

dev/bots/check_code_samples.dart

@@ -334,7 +334,6 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/widgets/navigator/navigator_state.restorable_push.0_test.dart',
   'examples/api/test/widgets/focus_manager/focus_node.unfocus.0_test.dart',
   'examples/api/test/widgets/framework/build_owner.0_test.dart',
-  'examples/api/test/widgets/framework/error_widget.0_test.dart',
   'examples/api/test/widgets/autofill/autofill_group.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/lib/widgets/framework/error_widget.0.dart

@@ -16,15 +16,7 @@ void main() {
       return ErrorWidget(details.exception);
     }
     // In release builds, show a yellow-on-blue message instead:
-    return Container(
-      alignment: Alignment.center,
-      child: Text(
-        'Error!\n${details.exception}',
-        style: const TextStyle(color: Colors.yellow),
-        textAlign: TextAlign.center,
-        textDirection: TextDirection.ltr,
-      ),
-    );
+    return ReleaseModeErrorWidget(details: details);
   };
 
   // Start the app.
@@ -69,3 +61,21 @@ class _ErrorWidgetExampleAppState extends State<ErrorWidgetExampleApp> {
     }
   }
 }
+
+class ReleaseModeErrorWidget extends StatelessWidget {
+  const ReleaseModeErrorWidget({super.key, required this.details});
+
+  final FlutterErrorDetails details;
+
+  @override
+  Widget build(BuildContext context) {
+    return Center(
+      child: Text(
+        'Error!\n${details.exception}',
+        style: const TextStyle(color: Colors.yellow),
+        textAlign: TextAlign.center,
+        textDirection: TextDirection.ltr,
+      ),
+    );
+  }
+}

examples/api/test/widgets/framework/error_widget.0_test.dart

@@ -0,0 +1,55 @@
+// 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/framework/error_widget.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('ErrorWidget is displayed in debug mode', (WidgetTester tester) async {
+    final ErrorWidgetBuilder oldBuilder = ErrorWidget.builder;
+    ErrorWidget.builder = (FlutterErrorDetails details) {
+       return ErrorWidget(details.exception);
+    };
+    await tester.pumpWidget(const example.ErrorWidgetExampleApp());
+
+    expect(find.widgetWithText(AppBar, 'ErrorWidget Sample'), findsOne);
+
+    await tester.tap(find.widgetWithText(TextButton, 'Error Prone'));
+    await tester.pump();
+
+    expectLater(tester.takeException(), isInstanceOf<Exception>());
+
+    final Finder errorWidget = find.byType(ErrorWidget);
+    expect(errorWidget, findsOneWidget);
+    final ErrorWidget error = tester.firstWidget(errorWidget);
+    expect(error.message, 'Exception: oh no, an error');
+
+    // Restore the ErrorWidget to conclude the test.
+    ErrorWidget.builder = oldBuilder;
+  });
+
+  testWidgets('ErrorWidget is displayed in release mode', (WidgetTester tester) async {
+    final ErrorWidgetBuilder oldBuilder = ErrorWidget.builder;
+    ErrorWidget.builder = (FlutterErrorDetails details) {
+      return example.ReleaseModeErrorWidget(details: details);
+    };
+    await tester.pumpWidget(const example.ErrorWidgetExampleApp());
+
+    expect(find.widgetWithText(AppBar, 'ErrorWidget Sample'), findsOne);
+
+    await tester.tap(find.widgetWithText(TextButton, 'Error Prone'));
+    await tester.pump();
+
+    expectLater(tester.takeException(), isInstanceOf<Exception>());
+
+    final Finder errorTextFinder = find.textContaining('Error!\nException: oh no, an error');
+    expect(errorTextFinder, findsOneWidget);
+    final Text errorText = tester.firstWidget(errorTextFinder);
+    expect(errorText.style?.color, Colors.yellow);
+
+    // Restore the ErrorWidget to conclude the test.
+    ErrorWidget.builder = oldBuilder;
+  });
+}