Add test for AutofillGroup api example (#156439)

Write Tests for API Examples of `autoffil_group`  as part  of https://github.com/flutter/flutter/issues/130459

This are tests of snippets used in [AutofillGroup class](https://api.flutter.dev/flutter/widgets/AutofillGroup-class.html)

dev/bots/check_code_samples.dart

@@ -330,7 +330,6 @@ 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/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/test/widgets/media_query/media_query_data.system_gesture_insets.0_test.dart',

examples/api/test/widgets/autofill/autofill_group.0_test.dart

@@ -0,0 +1,102 @@
+// 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/autofill/autofill_group.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('AutofillGroupExample renders and updates correctly', (WidgetTester tester) async {
+    await tester.pumpWidget(const example.AutofillGroupExampleApp());
+
+    expect(find.text('Shipping address'), findsOneWidget);
+    expect(find.text('Billing address'), findsOneWidget);
+    expect(find.byType(TextField), findsNWidgets(5));
+    expect(find.byType(Checkbox), findsOneWidget);
+    expect(find.text('Contact Phone Number'), findsOneWidget);
+
+    final Checkbox checkbox = tester.widget(find.byType(Checkbox));
+    expect(checkbox.value, isTrue);
+
+    // Tap to uncheck the checkbox (to show billing address fields).
+    await tester.tap(find.byType(Checkbox));
+    await tester.pump();
+
+    expect(
+      find.byType(AutofillGroup),
+      findsNWidgets(3), // 3 AutofillGroup widgets created
+    );
+
+    expect(
+      find.byType(TextField),
+      findsNWidgets(7), // 5 initial + 2 billing address fields
+    );
+
+    final TextField shippingAddress1 = tester.widget(
+      find.byType(TextField).at(0),
+    );
+    expect(
+      shippingAddress1.autofillHints,
+      contains(AutofillHints.streetAddressLine1),
+    );
+
+    final TextField shippingAddress2 = tester.widget(
+      find.byType(TextField).at(1),
+    );
+    expect(
+      shippingAddress2.autofillHints,
+      contains(AutofillHints.streetAddressLine2),
+    );
+
+    final TextField billingAddress1 = tester.widget(
+      find.byType(TextField).at(2),
+    );
+    expect(
+      billingAddress1.autofillHints,
+      contains(AutofillHints.streetAddressLine1),
+    );
+
+    final TextField billingAddress2 = tester.widget(
+      find.byType(TextField).at(3),
+    );
+    expect(
+      billingAddress2.autofillHints,
+      contains(AutofillHints.streetAddressLine2),
+    );
+
+    // Credit card information fields.
+    final TextField creditCardNumber = tester.widget(
+      find.byType(TextField).at(4),
+    );
+    expect(
+      creditCardNumber.autofillHints,
+      contains(AutofillHints.creditCardNumber),
+    );
+
+    final TextField creditCardSecurityCode = tester.widget(
+      find.byType(TextField).at(5),
+    );
+    expect(
+      creditCardSecurityCode.autofillHints,
+      contains(AutofillHints.creditCardSecurityCode),
+    );
+
+    // Contact phone number field.
+    final TextField phoneNumber = tester.widget(
+      find.byType(TextField).at(6),
+    );
+    expect(
+      phoneNumber.autofillHints,
+      contains(AutofillHints.telephoneNumber),
+    );
+
+    await tester.tap(find.byType(Checkbox));
+    await tester.pump();
+
+    expect(
+      find.byType(TextField),
+      findsNWidgets(5),
+    );
+  });
+}