how do you test a flutter block that consumes a stream

Question

i have a bloc that listens to a stream for authentication events (listening for firebase user events). my block is;

class AuthenticationBloc
    extends Bloc<AuthenticationEvent, AuthenticationLoadingState> {
  StreamSubscription<AuthenticationDetail> streamSubscription;
  CheckAuthenticationStatus authenticationStatus;

  AuthenticationBloc({@required CheckAuthenticationStatus authenticationStatus})
      : assert(authenticationStatus != null),
        assert(authenticationStatus.getStream() != null),
        this.authenticationStatus = authenticationStatus,
        super(AuthenticationLoadingState().init()) {
    this.streamSubscription = this
        .authenticationStatus
        .getStream()
        .listen((AuthenticationDetail detail) async* {
          print(detail.toString());
      add(StatusChanged(detail));
    });
  }

  @override
  Stream<AuthenticationLoadingState> mapEventToState(
      AuthenticationEvent event) async* {
    if (event is ListenToAuthenticationEvents) {
      print('well well well');
    } else if (event is StatusChanged) {
      print('yeeee');
    }
  }

  @override
  Future<void> close() {
    this.streamSubscription?.cancel();
    return super.close();
  }

  Future<AuthenticationLoadingState> init() async {
    return state.clone();
  }
}

And the providing use case is;

class CheckAuthenticationStatus
    implements UseCaseListner<AuthenticationDetail> {
  final AuthenticationRepository authenticationRepository;

  CheckAuthenticationStatus({@required this.authenticationRepository});

  @override
  Stream<AuthenticationDetail> getStream() =>
      authenticationRepository.getAuthDetailStream();
}

Im trying to write a bloc test where i can mock the usecase and add my own stream which i can send events to as follows;

class MockCheckAuthenticationStatus extends Mock
    implements CheckAuthenticationStatus {}

void main() {

  MockCheckAuthenticationStatus authenticationStatus;
  AuthenticationBloc authenticationBloc;
  StreamController controller;
  Stream<AuthenticationDetail> stream;

  setUp(() {
    controller = StreamController<AuthenticationDetail>();
    stream = controller.stream;
    authenticationStatus = MockCheckAuthenticationStatus();

  });


  test('initial state is correct', () async {
    var authenticationDetail = AuthenticationDetail(isValid: true);
    when(authenticationStatus.getStream()).thenAnswer((_) => stream);
    authenticationBloc =
        AuthenticationBloc(authenticationStatus: authenticationStatus);
//this should action, but doesnt, why?
    controller.add(authenticationDetail);
    await untilCalled(authenticationStatus.getStream());
    verify(authenticationStatus.getStream());

  });
tearDown(() {
    authenticationBloc?.close();
    controller?.close();
  });
}

the expectation is that controller.add(authenticationDetail) will generate the events and i expect to go to the mapEventToState on those events in the bloc. this is however not happening.

In short, how can i test the bloc by sending it stream events rather than programatically using bloc.add() events.

Answer 1

The premise of the question is based on the official Firebase auth documentation which states

Events are fired when the following occurs:

 - Right after the listener has been registered. 
 - When a user is signed in. 
 - When the current user is signed out.

So instead of registering a listener , then calling getUser through an event. Just registering the listener should also trigger the first event which we can then use to navigate accordingly. The intent of my test was to simulate this first event.

The bug in the code was the async* on the line .listen((AuthenticationDetail detail) async* { in the AuthenticationBloc constructor