Bloc: Tests are crashing after switching to 1.0.0 from 0.19.0

[Den-Ree]

Describe the bug
The tests are failed with the following error when I'm testing widget with MultiBlocListener on v1.0.0.

Exception has occurred.
TestFailure (Expected: exactly one matching node in the widget tree
  Actual: ?:<zero widgets with key [<'EMAIL_LOGIN_EMAIL_TEXT_FIELD'>] (ignoring offstage widgets)>
   Which: means none were found but one was expected
)

To Reproduce
Steps to reproduce the behavior:

1. Mock block and run tests
2. Widget is build but during run it doesn't go to builder: (BuildContext context, LoginState loginState)
3. As result widget is not build correctly
4. The error occurs.

Expected behavior
In version 0.19.0 it goes to the builder: (BuildContext context, LoginState loginState) and build the widget.

Test

setUp(() {
    authBloc = MockAuthenticationBloc();
    loginBloc = MockLoginBloc();

    testWidget = wrapWidget(Scaffold(
        body: BlocProvider.value(
          value: loginBloc,
          child: EmailLoginForm(authBloc: authBloc, loginBloc: loginBloc),
        )
    ), null);
  });

testWidgets('form is initially displayed', (WidgetTester tester) async {
    when(loginBloc.state).thenAnswer((_) => LoginState.loading());

    await tester.pumpWidget(testWidget);
    await tester.pumpAndSettle(); // to wait for localization

    expect(find.byKey(EMAIL_LOGIN_EMAIL_TEXT_FIELD), findsOneWidget);
    expect(find.byKey(EMAIL_LOGIN_PASSWORD_TEXT_FIELD), findsOneWidget);
    expect(find.byKey(EMAIL_LOGIN_SUBMIT_BUTTON), findsOneWidget);
  });

Widget

@override
  Widget build(BuildContext context) {
    return MultiBlocListener(
      listeners: [
        BlocListener<LoginBloc, LoginState>(
          bloc: _loginBloc,
          listener: (context, state) {
            if (_loginSucceeded(state)) {
              widget.tracker.trackEvent(event: Events.LOGIN_SUCCESS);
              _authBloc.onLogin(token: state.token);
            }
          },
        ),
        BlocListener<AuthenticationBloc, AuthenticationState>(
          bloc: _authBloc,
          listener: (context, state) {
            if (state.isAuthenticated) {
              Navigator.pushReplacementNamed(context, Constants.ROUTE_HOME);
            }
          },
        ),
      ],
      child: BlocBuilder<LoginBloc, LoginState>(
        bloc: _loginBloc,
        builder: (BuildContext context, LoginState loginState) {
          if (_loginFailed(loginState)) {
            buttonEnabled = true;
            widget.tracker.trackEvent(event: Events.LOGIN_FAILED);

            onWidgetDidBuild(() {
              final String errorMessage = _isNetworkError(loginState.error)
                  ? AppLocalizations.of(context).loginNetworkErrorMessage
                  : AppLocalizations.of(context).loginErrorMessage;
              _displayLoginErrorDialog(errorMessage);
            });
          }

          return _form(loginState);
        },
      ),
    );
  }

*Logs *
There is no errors in flutter analyze and flutter doctor

[felangel]

Hi @Den-Ree 👋
Thanks for opening an issue!

The problem is in 1.0.0 you no longer access the state stream via bloc.state because the bloc itself extends Stream.

You need to change when(loginBloc.state).thenAnswer((_) => LoginState.loading());

to

whenListen(loginBloc, Stream<LoginState>.fromIterable([LoginState.loading()));

whenListen comes from the bloc_test package.

Hope that helps and sorry for any inconvenience!

[Den-Ree]

@felangel thanks for the answer. But the problem is still happens. When I debug the test then code never go to inside. If I correctly understand that it should be called during building the widget or not?

builder: (BuildContext context, LoginState loginState) {
....
}

[felangel]

If you want to just mock the current state of the bloc you can do:

when(bloc.state).thenReturn(LoginState.loading());

Use whenListen if you want to mock the bloc stream. In your test you will likely need to do something like:

// Set the bloc's stream to empty
whenListen(loginBloc, Stream<LoginState>.empty());
// Set the bloc's state to Loading
when(loginBloc.state).thenReturn(LoginState.loading());

Hope that helps 👍

[Den-Ree]

@felangel thanks a lot for the help, it works as you suggested. But I noticed the following thing, which is not clear for me.

During running the test, the first time state are null in
builder: (BuildContext context, LoginState loginState)

and only for the second time I get the needed state.

[felangel]

@Den-Ree can you please provide a link to a sample app which illustrates the issue you're seeing? If you're initially seeing a null state that means that the bloc's state has not been properly stubbed. Are you using when(loginBloc.state).thenReturn(LoginState.loading());?