Bloc: How to test /flutter_firestore_todos bloc example

[adamsmaka]

In provided example todos_bloc.dart has code like that:

@override
  Stream<TodosState> mapEventToState(TodosEvent event) async* {
    if (event is LoadTodos) {
      yield* _mapLoadTodosToState();
    } else if (event is TodosUpdated) {
      yield* _mapTodosUpdateToState(event);
    }
  }

  Stream<TodosState> _mapLoadTodosToState() async* {
    _todosSubscription?.cancel();
    _todosSubscription = _todosRepository.todos().listen(
          (todos) => add(TodosUpdated(todos)),
        );
  }

  Stream<TodosState> _mapTodosUpdateToState(TodosUpdated event) async* {
    yield TodosLoaded(event.todos);
  }

So I would expect to write a test like this:

group('LoadTodos', () {
    blocTest(
      'should emit [TodosLoaded] state',
      build: () async => TodosBloc(todosRepository: mockTodosRepository),
      act: (bloc) => bloc.add(LoadTodos()),
      expect: [
        isA<TodosLoaded>(),
      ],
    );
  });

but it doesn't pass. No events are emitted even if I mock the repository.todos() response. I would like to catch the state from the repository stream. Can you help me with it?

[felangel]

HI @adamsmaka 👋
Thanks for opening an issue!

Are you able to share a link to the failing test? I'm happy to open a pull request with suggestions, thanks 👍

[adamsmaka]

Hi @felangel , thanks for quick reply.
Of course, here is a failing test:

import 'package:bloc_test/bloc_test.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:mockito/mockito.dart';

import '../lib/blocs/todos/todos_bloc.dart';
import '../lib/blocs/todos/todos_event.dart';
import '../lib/blocs/todos/todos_state.dart';
import '../todos_repository/lib/todos_repository.dart';

class MockTodosRepository extends Mock implements TodosRepository {}

main() {
  MockTodosRepository mockTodosRepository;
  setUp(() {
    mockTodosRepository = MockTodosRepository();
  });

  TodosBloc getSut() {
    when(mockTodosRepository.todos())
        .thenAnswer((_) => Stream<List<Todo>>.value([]));
    return TodosBloc(todosRepository: mockTodosRepository);
  }

  group('Load', () {
    blocTest(
      'should emit [TodosLoading, TodosLoaded] states',
      build: () async => getSut(),
      act: (bloc) => bloc.add(LoadTodos()),
      expect: [
        isA<TodosLoaded>(),
      ],
    );
  });
}

[felangel]

@adamsmaka no problem! Can you try to provide a wait with Duration.zero?

blocTest(
  '...',
  build: () async => getSut(),
  act: (bloc) => bloc.add(LoadTodos()),
  wait: Duration.zero,
  expect: [isA<TodosLoaded>()],
)

Let me know if that works. I believe this should be resolved in the upcoming release and you can test it in v7.0.0-dev.2 of bloc_test.

[adamsmaka]

wait: Duration.zero helped! thank you.
Also tried bloc_test 7.0.0-dev.2 and it also works. I like that it doesn't require async on build anymore. But is it intentional that it doesn't recognise initial state anymore?

[felangel]

@adamsmaka that's great to hear! Yeah it's intentional because blocs no longer emit the current state upon subscription 👍

[adamsmaka]

Ok so problem solved. Thank you so much, appreciate your work. Bloc library is awesome.

[felangel]

No problem! Regarding the initial state I recommend writing a separate test for it like:

test('initial state is...', () {
  expect(MyBloc().state, InitialState());
});

Thanks so much for the positive feedback, I really appreciate it 🙏 💙