How to unit test Flowable.interval?

I have the following code inside the presenter.

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public class SignUpPresenter implements Presenter {

  private CompositeDisposable disposables;
  private View view;

  @Inject public SignUpPresenter() {
  }

  public void setView(View view) {
    this.view = view;
  }

  public void redirectToLogInScreenAfterOneSecond() {
    disposables = RxUtil.initDisposables(disposables);

    view.displaySuccessMessage();

    Disposable disposable = Flowable.interval(1, TimeUnit.SECONDS)
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(aLong -> view.onRegistrationSuccessful(), view::handleError);

    disposables.add(disposable);
  }

  @Override public void dispose() {
    RxUtil.dispose(disposables);
  }

  public interface View extends Presenter.View {

    void onRegistrationSuccessful();

    void displaySuccessMessage();
  }
}

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Now, I want to write unit test for that method.

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@RunWith(PowerMockRunner.class)
public class SignUpPresenterTest {

  @Rule TrampolineSchedulerRule trampolineSchedulerRule = new TrampolineSchedulerRule();

  @Mock SignUpPresenter.View view;

  private SignUpPresenter presenter;
  private TestScheduler testScheduler;

  @Before public void setUp() {
    testScheduler = new TestScheduler();
    RxJavaPlugins.setComputationSchedulerHandler(scheduler -> testScheduler);
    presenter = new SignUpPresenter();
    presenter.setView(view);
  }

  @Test public void shouldDisplaySuccessMessage() {
    testScheduler.advanceTimeTo(1, TimeUnit.SECONDS);
    presenter.redirectToLogInScreenAfterOneSecond();
    Mockito.verify(view).displaySuccessMessage();
    Mockito.verify(view).onRegistrationSuccessful();
  }
}

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Here is the error that I get:

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Wanted but not invoked:
view.onRegistrationSuccessful();
-> at com.test.presentation.signup.SignUpPresenterTest.shouldDisplaySuccessMessage(SignUpPresenterTest.java:36)

However, there were other interactions with this mock:
view.displaySuccessMessage();
-> at com.test.presentation.signup.SignUpPresenter.redirectToLogInScreenAfterOneSecond(SignUpPresenter.java:28)


Wanted but not invoked:
view.onRegistrationSuccessful();
-> at com.test.presentation.signup.SignUpPresenterTest.shouldDisplaySuccessMessage(SignUpPresenterTest.java:36)

However, there were other interactions with this mock:
view.displaySuccessMessage();
-> at com.test.presentation.signup.SignUpPresenter.redirectToLogInScreenAfterOneSecond(SignUpPresenter.java:28)

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How I can solve this?

You have to move the time after the flow setup:

@Test public void shouldDisplaySuccessMessage() {
    presenter.redirectToLogInScreenAfterOneSecond();
    testScheduler.advanceTimeTo(1, TimeUnit.SECONDS);

    Mockito.verify(view).displaySuccessMessage();
    Mockito.verify(view).onRegistrationSuccessful();
}

Also you don't need that many operators after interval but use the mainThread scheduler directly:

Disposable disposable = Flowable.interval(1, TimeUnit.SECONDS, AndroidSchedulers.mainThread())
    .subscribe(aLong -> view.onRegistrationSuccessful(), view::handleError);

and replace the mainThread scheduler:

@Before public void setUp() {
    testScheduler = new TestScheduler();
    RxAndroidPlugins.setMainThreadSchedulerHandler(scheduler -> testScheduler);
    presenter = new SignUpPresenter();
    presenter.setView(view);
}