android - Verify interactions in rxjava subscribers

Question

Picture the situation in an MVP pattern where your presenter subscribes to a service returning an observer:

public void gatherData(){
   service.doSomeMagic()
      .observeOn(Schedulers.io())
      .subscribeOn(AndroidSchedulers.mainThread())
      .subscribe(new TheSubscriber());
}

Now the class TheSubscriber calls onNext a method from the view, say:

@Override public void onNext(ReturnValue value) {
  view.displayWhatever(value);
}

Now, in my unit test I would like to verify that when the method gatherData() is called on a non-erroneous situation, the view's method displayWhatever(value) is called.

The question:

Is there a clean way to do this?

Background:

• I'm using mockito to verify the interactions and a lot more of course
• Dagger is injecting the entire presenter except for TheSubscriber

What have I tried:

• Inject the subscriber and mock it in the tests. Looks a bit dirty to me, because if I want to change the way the presenter interacts with the service (Say not Rx) then I need to change a lot of tests and code.
• Mock the entire service. This was not so bad, but requires me to mock a lot of methods and I didn't quite reach what I wanted.
• Looked up around the internet, but no one seems to have a clean straight way of doing this

Thanks for the help

Answer 1

Assuming that you are using interfaces for service and view in a similar manner:

class Presenter{
  Service service;
  View view;

  Presenter(Service service){
    this.service = service;
  }

  void bindView(View view){
    this.view = view;
  }

  void gatherData(){
    service.doSomeMagic()
      .observeOn(Schedulers.io())
      .subscribeOn(AndroidSchedulers.mainThread())
      .subscribe(view::displayValue);
  }
}

It is possible then to provide mock to control and verify behaviour:

@Test void assert_that_displayValue_is_called(){
  Service service = mock(Service.class);
  View view = mock(View.class);
  when(service.doSomeMagic()).thenReturn(Observable.just("myvalue"));
  Presenter presenter = new Presenter(service);
  presenter.bindView(view);

  presenter.gatherData();

  verify(view).displayValue("myvalue");
}