@Test public void lightService_add() { String LIGHT_UUID = "myUuid"; LightModel lightModel = new LightModel(); when(lightRepository.add(lightModel)).thenReturn(Observable.just(LIGHT_UUID)); TestSubscriber<String> tester = new TestSubscriber<>(); lightService.add(lightModel).subscribe(tester); verify(lightRepository).add(lightModel); tester.assertValue(LIGHT_UUID); tester.assertCompleted(); tester.assertNoErrors(); }