@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();
  }