Add test for search_anchor.0.dart (#152371)

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

It adds a test for
- `examples/api/lib/material/search_anchor/search_anchor.0.dart`

examples/api/test/material/search_anchor/search_anchor.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/material/search_anchor/search_anchor.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Search a color in the search bar and choosing an option changes the color scheme', (WidgetTester tester) async {
+    await tester.pumpWidget(const example.SearchBarApp());
+
+    expect(find.widgetWithText(AppBar, 'Search Bar Sample'), findsOne);
+
+    expect(find.byWidgetPredicate((Widget widget) => widget is Card && widget.color ==const Color(0xff6750a4)), findsOne);
+
+    await tester.tap(find.byIcon(Icons.search));
+    await tester.pumpAndSettle();
+
+    expect(find.text('No search history.'), findsOne);
+    await tester.enterText(find.byType(SearchBar).last, 're');
+    await tester.pump();
+
+    expect(find.widgetWithText(ListTile, 'red'), findsOne);
+    expect(find.widgetWithText(ListTile, 'green'), findsOne);
+    expect(find.widgetWithText(ListTile, 'grey'), findsOne);
+
+    await tester.tap(find.widgetWithText(ListTile, 'red'));
+    await tester.pumpAndSettle();
+
+    expect(find.byWidgetPredicate((Widget widget) => widget is Card && widget.color ==const Color(0xff904a42)), findsOne);
+
+    await tester.tap(find.byIcon(Icons.search));
+    await tester.pumpAndSettle();
+
+    await tester.tap(find.byIcon(Icons.close));
+    await tester.pump();
+
+    expect(find.widgetWithText(ListTile, 'red'), findsOne, reason: 'The search history should be displayed');
+    expect(find.widgetWithIcon(ListTile, Icons.history), findsOne);
+
+    await tester.enterText(find.byType(SearchBar).last, 'b');
+    await tester.pump();
+
+    expect(find.widgetWithText(ListTile, 'blue'), findsOne);
+    expect(find.widgetWithText(ListTile, 'beige'), findsOne);
+    expect(find.widgetWithText(ListTile, 'brown'), findsOne);
+    expect(find.widgetWithText(ListTile, 'black'), findsOne);
+
+    await tester.tap(find.widgetWithText(ListTile, 'blue'));
+    await tester.pumpAndSettle();
+
+    expect(find.byWidgetPredicate((Widget widget) => widget is Card && widget.color ==const Color(0xff36618e)), findsOne);
+  });
+}