Add tests for stream_builder.0.dart API example. (#147832)

This PR contributes to https://github.com/flutter/flutter/issues/130459

### Description
- Updates `examples/api/lib/widgets/async/stream_builder.0.dart`
- Adds test for `examples/api/lib/widgets/async/stream_builder.0.dart`

dev/bots/check_code_samples.dart

@@ -405,7 +405,6 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/widgets/nested_scroll_view/nested_scroll_view.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/async/stream_builder.0_test.dart',
   'examples/api/test/widgets/async/future_builder.0_test.dart',
   'examples/api/test/widgets/restoration_properties/restorable_value.0_test.dart',
   'examples/api/test/widgets/animated_size/animated_size.0_test.dart',

examples/api/lib/widgets/async/stream_builder.0.dart

@@ -13,34 +13,54 @@ void main() => runApp(const StreamBuilderExampleApp());
 class StreamBuilderExampleApp extends StatelessWidget {
   const StreamBuilderExampleApp({super.key});
 
+  static const Duration delay = Duration(seconds: 1);
+
   @override
   Widget build(BuildContext context) {
     return const MaterialApp(
-      home: StreamBuilderExample(),
+      home: StreamBuilderExample(delay: delay),
     );
   }
 }
 
 class StreamBuilderExample extends StatefulWidget {
-  const StreamBuilderExample({super.key});
+  const StreamBuilderExample({
+    required this.delay,
+    super.key,
+  });
+
+  final Duration delay;
 
   @override
   State<StreamBuilderExample> createState() => _StreamBuilderExampleState();
 }
 
 class _StreamBuilderExampleState extends State<StreamBuilderExample> {
-  final Stream<int> _bids = (() {
+  late final StreamController<int> _controller = StreamController<int>(
-    late final StreamController<int> controller;
-    controller = StreamController<int>(
     onListen: () async {
-        await Future<void>.delayed(const Duration(seconds: 1));
+      await Future<void>.delayed(widget.delay);
-        controller.add(1);
+
-        await Future<void>.delayed(const Duration(seconds: 1));
+      if (!_controller.isClosed) {
-        await controller.close();
+        _controller.add(1);
+      }
+
+      await Future<void>.delayed(widget.delay);
+
+      if (!_controller.isClosed) {
+        _controller.close();
+      }
     },
   );
-    return controller.stream;
+
-  })();
+  Stream<int> get _bids => _controller.stream;
+
+  @override
+  void dispose() {
+    if (!_controller.isClosed) {
+      _controller.close();
+    }
+    super.dispose();
+  }
 
   @override
   Widget build(BuildContext context) {
@@ -50,8 +70,24 @@ class _StreamBuilderExampleState extends State<StreamBuilderExample> {
       child: Container(
         alignment: FractionalOffset.center,
         color: Colors.white,
-        child: StreamBuilder<int>(
+        child: BidsStatus(bids: _bids),
-          stream: _bids,
+      ),
+    );
+  }
+}
+
+class BidsStatus extends StatelessWidget {
+  const BidsStatus({
+    required this.bids,
+    super.key,
+  });
+
+  final Stream<int>? bids;
+
+  @override
+  Widget build(BuildContext context) {
+    return StreamBuilder<int>(
+      stream: bids,
       builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
         List<Widget> children;
         if (snapshot.hasError) {
@@ -67,7 +103,11 @@ class _StreamBuilderExampleState extends State<StreamBuilderExample> {
             ),
             Padding(
               padding: const EdgeInsets.only(top: 8),
-                  child: Text('Stack trace: ${snapshot.stackTrace}'),
+              child: Text(
+                'Stack trace: ${snapshot.stackTrace}',
+                maxLines: 1,
+                overflow: TextOverflow.ellipsis,
+              ),
             ),
           ];
         } else {
@@ -117,7 +157,11 @@ class _StreamBuilderExampleState extends State<StreamBuilderExample> {
                 ),
                 Padding(
                   padding: const EdgeInsets.only(top: 16),
-                      child: Text('\$${snapshot.data} (closed)'),
+                  child: Text(
+                    snapshot.hasData
+                        ? '\$${snapshot.data} (closed)'
+                        : '(closed)',
+                  ),
                 ),
               ];
           }
@@ -128,8 +172,6 @@ class _StreamBuilderExampleState extends State<StreamBuilderExample> {
           children: children,
         );
       },
-        ),
-      ),
     );
   }
 }

examples/api/test/widgets/async/stream_builder.0_test.dart

@@ -0,0 +1,110 @@
+// 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 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/widgets/async/stream_builder.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.StreamBuilderExampleApp(),
+    );
+
+    expect(find.byType(CircularProgressIndicator), findsOneWidget);
+    expect(find.text('Awaiting bids...'), findsOneWidget);
+
+    await tester.pump(example.StreamBuilderExampleApp.delay);
+
+    expect(find.byIcon(Icons.check_circle_outline), findsOneWidget);
+    expect(find.text(r'$1'), findsOneWidget);
+
+    await tester.pump(example.StreamBuilderExampleApp.delay);
+
+    expect(find.byIcon(Icons.info), findsOneWidget);
+    expect(find.text(r'$1 (closed)'), findsOneWidget);
+  });
+
+  testWidgets('BidsStatus correctly displays error state', (WidgetTester tester) async {
+    final StreamController<int> controller = StreamController<int>();
+    addTearDown(controller.close);
+
+    controller.onListen = () {
+      controller.addError('Unexpected error!', StackTrace.empty);
+    };
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: example.BidsStatus(bids: controller.stream),
+      ),
+    );
+    await tester.pump();
+
+    expect(find.byIcon(Icons.error_outline), findsOneWidget);
+    expect(find.text('Error: Unexpected error!'), findsOneWidget);
+    expect(find.text('Stack trace: ${StackTrace.empty}'), findsOneWidget);
+  });
+
+  testWidgets('BidsStatus correctly displays none state', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const MaterialApp(
+        home: example.BidsStatus(bids: null),
+      ),
+    );
+
+    expect(find.byIcon(Icons.info), findsOneWidget);
+    expect(find.text('Select a lot'), findsOneWidget);
+  });
+
+  testWidgets('BidsStatus correctly displays waiting state', (WidgetTester tester) async {
+    final StreamController<int> controller = StreamController<int>();
+    addTearDown(controller.close);
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: example.BidsStatus(bids: controller.stream),
+      ),
+    );
+
+    expect(find.byType(CircularProgressIndicator), findsOneWidget);
+    expect(find.text('Awaiting bids...'), findsOneWidget);
+  });
+
+  testWidgets('BidsStatus correctly displays active state', (WidgetTester tester) async {
+    final StreamController<int> controller = StreamController<int>();
+    addTearDown(controller.close);
+
+    controller.onListen = () {
+      controller.add(1);
+    };
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: example.BidsStatus(bids: controller.stream),
+      ),
+    );
+    await tester.pump();
+
+    expect(find.byIcon(Icons.check_circle_outline), findsOneWidget);
+    expect(find.text(r'$1'), findsOneWidget);
+  });
+
+  testWidgets('BidsStatus correctly displays done state', (WidgetTester tester) async {
+    final StreamController<int> controller = StreamController<int>();
+    controller.close();
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: example.BidsStatus(bids: controller.stream),
+      ),
+    );
+    await tester.pump();
+
+    expect(find.byIcon(Icons.info), findsOneWidget);
+    expect(find.text('(closed)'), findsOneWidget);
+  });
+}