How to use Mockito to verify stream callback - unit-testing

Question

I developing an application an flutter and use clean architecture.
I created a use case return a List from a stream. The stream sends the List from an observer. Above is the code:
abstract class GetAllServicesObserver implements Observer {
void onGetAllSuccess(List<Service> services);
void onGetAllError(Exception error);
}
class GetAllServices extends UseCase<GetAllServicesObserver, NoParams> {
final User _user;
final ServiceRepository _serviceRepository;
StreamSubscription _subscription;
GetAllServices({
#required User user,
#required ServiceRepository serviceRepository,
}) : _user = user,
_serviceRepository = serviceRepository;
#override
action(observer, params) async {
_subscription?.cancel();
final _stream = _serviceRepository.all(_user);
_subscription = _stream.listen((services) {
observer.onGetAllSuccess(services);
}, onError: (e) {
observer.onGetAllError(e);
});
}
}
And I created an unit test to this use case:
test('should to return all services', () {
//setup
when(repository.all(user)).thenAnswer((_) async* {
yield List<Service>();
});
final useCase = GetAllServices(user: user, serviceRepository: repository);
useCase.observer = observer;
//run
useCase();
//verify
verify(observer.onGetAllSuccess(List<Service>()));
});
}
But it's returns the follow message and not pass:
ERROR: No matching calls (actually, no calls at all).
(If you called verify(...).called(0);, please instead use verifyNever(...);.)
Would anyone know what the problem is?

Answer 1

Have you tried untilCalled before verify? e.g.:
await untilCalled(some method that will be called)