如何使用 MockBloc 实现小部件测试？

Question

我正在尝试实现小部件测试以测试登录表单。这个测试取决于我使用 MockBloc 模拟的一个块。但是，它会引发以下错误：

══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK╞════════════════════════════════════════════════════
The following StateError was thrown running a test:
Bad state: No method stub was called from within `when()`. Was a real method called, or perhaps an 
extension method?

我在下面的link 中发现了一个类似的错误，但我看不出它如何帮助我解决我的问题。

我还查看了以下file on gitlub，这是使用 bloc_test 进行小部件测试的示例。该链接可以在 Bloc 图书馆的官方网站上找到 - 特别是在Todos App in Flutter using the Bloc library。

但是，该示例使用的是bloc_test: ^3.0.1，而我使用的是bloc_test: ^8.0.0，可以找到here。

这是一个最小的例子：

• 登录表单小部件

class LoginForm extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Form(
      key: '_loginForm',
      child: Column(
        children: <Widget>[
           ...
           BlocConsumer<AuthenticationBloc, AuthenticationState>(
             listener: (context, state) {
               ...
             },
             builder: (context, state) {
               if (state is AuthenticationInitial) {
                 ...
               } else if (state is LoggingIn || state is LoggedIn) {
                 ...
               } else if (state is Error) { 
                 return Column(
                  children: <Widget>[
                    ...
                    Message(
                      message: state.message,
                      messageContainerWidth: 290,
                      messageContainerHeight: 51,
                    ),
                    ...
                  ],
                );
               }
             }
           ),
        ],
      ),
    );
  }
}

• 消息小部件

class Message extends StatelessWidget {
  final String message;
  final double messageContainerWidth;
  final double messageContainerHeight;

  ...
  @override
  Widget build(BuildContext context) {
    return Container(
      width: messageContainerWidth,
      height: messageContainerHeight,
      child: Center(
        child: message != ""
            ? Text(
                message,
                textAlign: TextAlign.center,
                style: TextStyle(
                  color: Color.fromRGBO(242, 241, 240, 1),
                  fontSize: 15,
                ),
              )
            : child,
      ),
    );
  }
}

• 小部件测试（我想测试验证状态为错误时是否显示消息）

...
import 'package:bloc_test/bloc_test.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:mocktail/mocktail.dart';
...

// Mocking my LoginUser usecase
class MockLoginUser extends Mock implements LoginUser {}

// Mocking my bloc
class MockAuthenticationBloc
    extends MockBloc<AuthenticationEvent, AuthenticationState>
    implements AuthenticationBloc {}

class AuthenticationStateFake extends Fake implements AuthenticationState {}

void main() {
  MockLoginUser mockLoginUser;

  setUpAll(() {
    registerFallbackValue<AuthenticationState>(AuthenticationStateFake());
  });

  setUp(() {
    mockLoginUser = MockLoginUser();
    authenticationBloc = AuthenticationBloc(loginUser: mockLoginUser);
  });

  group('Login', () {
    testWidgets(
        'should show a Message when the Authentication state is Error',
        (WidgetTester tester) async {
      whenListen(
        authenticationBloc,
        Stream.fromIterable(
          [
            LoggingIn(),
            Error(
              message: 'Some error message',
            ),
          ],
        ),
        initialState: AuthenticationInitial(),
      );
     
      final widget = LoginForm();
      await tester.pumpWidget(
         BlocProvider<AuthenticationBloc>(
          create: (context) => authenticationBloc,
          child: MaterialApp(
            title: 'Widget Test',
            home: Scaffold(body: widget),
          ),
        ),
      );
      await tester.pumpAndSettle();

      final messageWidget = find.byType(Message);
      expect(messageWidget, findsOneWidget);
    });
  });
}

如果有人可以帮助我解决错误，或者可以让我知道实现小部件测试的另一种方法，我将不胜感激。

提前致谢！

Answer 1

我解决了这个问题，我想分享答案，以防有人发现同样的问题。

首先，这个link 真的很有帮助。

解决方案是通过以下方式更改 Widget 测试：

...
import 'package:bloc_test/bloc_test.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:mocktail/mocktail.dart';
...

class MockAuthenticationBloc
    extends MockBloc<AuthenticationEvent, AuthenticationState>
    implements AuthenticationBloc {}

class AuthenticationStateFake extends Fake implements AuthenticationState {}

class AuthenticationEventFake extends Fake implements AuthenticationEvent {}

void main() {
  group('Login', () {

    setUpAll(() {
      registerFallbackValue<AuthenticationState>(AuthenticationStateFake());
      registerFallbackValue<AuthenticationEvent>(AuthenticationEventFake());
    });

    testWidgets(
        'should show a Message when the Authentication state is Error',
        (WidgetTester tester) async {
      // arrange
      final mockAuthenticationBloc = MockAuthenticationBloc();
      when(() => mockAuthenticationBloc.state).thenReturn(
        LoggingIn(), // the desired state
      );

      // find
      final widget = LoginForm();
      final messageWidget = find.byType(Message);

      // test
      await tester.pumpWidget(
         BlocProvider<AuthenticationBloc>(
          create: (context) => mockAuthenticationBloc,
          child: MaterialApp(
            title: 'Widget Test',
            home: Scaffold(body: widget),
          ),
        ),
      );
      await tester.pumpAndSettle();

      // expect
      expect(messageWidget, findsOneWidget);
    });
  });
}