MockTweeterApi.java

public class MockTweeterApi extends TweeterApi{
    public MockTweeterApi(Retrofit retrofit, LocalDataCache dataCache, Scheduler mainScheduler) {
        super(retrofit, dataCache, mainScheduler);
    }

    @Override
    public Observable<UserProfile> login(String username, String password) {
        return Observable.just(new UserProfile(username, password))
                .observeOn(mainScheduler);
    }

    @Override
    public Observable<Object> logout() {
        return Observable.just(null)
                .observeOn(mainScheduler);
    }
}