Flutter: BLoC, testing streams

Question

Testing the bloc pattern is not so clear to me. So, if I have these 2 stream controllers:

final _controller1 = StreamController();
final _controller2 = StreamController<bool>;

Sink get controller1Add = _controller1.sink;
Stream<bool> get controller2Out = _controller2.stream;

and I want to test that, from this function:

submit() {
if (_controller1.value == null ||
        _controller1.value.isEmpty) {
          print(...)
      return;
    }else
       _controller2.sink.add(true);
    }

the _controller2.stream should have true, how should I do?

I tried something like:

  test("test", (){
    bloc.submit();
    expect(bloc.controller2Out, emitsAnyOf([true]));
  });

but, of course, it didn´t work.

Solution

I've modified your code to use the RxDart's BehaviorSubject and it seems to work. You are using StreamController but I get error cause it doesn't have the value property.

final _controller1 = BehaviorSubject<String>();
final _controller2 = BehaviorSubject<bool>();

Sink get controller1Add => _controller1.sink;  
Stream<bool> get controller2Out => _controller2.stream;

  submit() {
    if (_controller1.value == null || _controller1.value.isEmpty) {
      print('Error');
      _controller2.sink.add(false);
      return;
    } else {
      print('OK');
      _controller2.sink.add(true);
    }
  }

The test:

bloc.controller1Add.add('');
bloc.submit();
expect(bloc.controller2Out, emits(false));

bloc.controller1Add.add('test');
bloc.submit();
expect(bloc.controller2Out, emits(true));

bloc.controller1Add.add('');
bloc.submit();
expect(bloc.controller2Out, emits(false));

Comments

[Günter Zöchbauer]

What if you move bloc.submit(); below the expect(...) line? If submit() is sync()` there won't be any event emitted to subscribers that subscribe only afterwards.

[Jordan Davies]

I think you have to make your test async and await the submit call.