Add test for radio.toggleable.0.dart (#149153)

Contributes to flutter/flutter#130459

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

dev/bots/check_code_samples.dart

@@ -339,7 +339,6 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/material/text_form_field/text_form_field.1_test.dart',
   'examples/api/test/material/scrollbar/scrollbar.1_test.dart',
   'examples/api/test/material/dropdown_menu/dropdown_menu.1_test.dart',
-  'examples/api/test/material/radio/radio.toggleable.0_test.dart',
   'examples/api/test/material/search_anchor/search_anchor.0_test.dart',
   'examples/api/test/material/search_anchor/search_anchor.1_test.dart',
   'examples/api/test/material/search_anchor/search_anchor.2_test.dart',

examples/api/test/material/radio/radio.toggleable.0_test.dart

@@ -0,0 +1,32 @@
+// 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/radio/radio.toggleable.0.dart'
+    as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('StreamBuilder listens to internal stream', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.ToggleableExampleApp(),
+    );
+
+    expect(find.byType(Radio<int>), findsExactly(5));
+    expect(find.text('Hercules Mulligan'), findsOne);
+    expect(find.text('Eliza Hamilton'), findsOne);
+    expect(find.text('Philip Schuyler'), findsOne);
+    expect(find.text('Maria Reynolds'), findsOne);
+    expect(find.text('Samuel Seabury'), findsOne);
+
+    for (int i = 0; i < 5; i++) {
+      await tester.tap(find.byType(Radio<int>).at(i));
+      await tester.pump();
+      expect(
+        find.byWidgetPredicate((Widget widget) => widget is Radio<int> && widget.groupValue == i),
+        findsExactly(5),
+      );
+    }
+  });
+}