通过单元测试如何测试 viewModel 中的 switchMap 从存储库类调用正确的方法

Question

In my ViewModel i have used swithcMap with a liveData varaible as parameter. When the liveData variable gets set/changed then the switchMap calls a method from my Repository. My viewModel code:

class MainViewModel @Inject constructor(val mainRepository: MainRepository) : ViewModel() {

    var searchQuery:MutableLiveData<SearchQuery> = MutableLiveData()
    var liveResult:MediatorLiveData<My_Result> = MediatorLiveData()


    var apiData:LiveData<My_Result> = Transformations
    .switchMap(searchQuery){query ->
        query?.let {
        val source: LiveData<My_Result> = mainRepository.fetchApiresultFromClient(it.filter_search , it.filter_topics, it.filter_language , it.page_number)

        liveResult.addSource(source){ item->
            liveResult.value = item
            liveResult.removeSource(source)
        }

        source

        }
    }

}

Now I want to test that if searchQuery is set then:

• switchMap is triggered
• and when switchMap is triggered then mainRepository.fetchApiresultFromClient(..) is called
• also if mainRepository.fetchApiresultFromClient(..) is called then the returned type is of LiveData

How do I do this? All I have managed to do is :

@ExtendWith(InstantExecutorExtension::class)
class MainViewModelTest {

    lateinit var  mainViewModel: MainViewModel

    @Mock
     lateinit var  mainRepository: MainRepository


    @BeforeEach
    fun init()  {
    MockitoAnnotations.initMocks(this)
    mainViewModel = MainViewModel(mainRepository)
    }


    @Test
    @Throws(Exception::class)
    fun setSearchQuery_callsRepositoryMethod() {
    var filter_search: SearchQuery = SearchQuery("java", "","",1)

    }

}

Answer 1

To make your code easier to test you could replace it by:

class MainViewModel @Inject constructor(val mainRepository: MainRepository) : ViewModel() {

    val searchQuery:MutableLiveData<SearchQuery> = MutableLiveData()

    var apiData:LiveData<My_Result> = Transformations.switchMap(searchQuery) { query ->
        query?.let {
            mainRepository.fetchApiresultFromClient(it.filter_search , it.filter_topics, it.filter_language , it.page_number)
        }
    }
}

Then you should

• mock mainRepository.fetchApiresultFromClient to return a MutableLiveData
• call mainViewModel.searchQuery.value = Query(...)
• and assert that when mainRepository emits a new value apiData also emits the same value.

If you have some test code to share I can help you to complete it