Android单元测试中如何调用回调？

Question

I want to invoke a callback to assert the execution it makes.

I'm using MVVM in my app. In one of the view models I implemented, I want to make sure the ui state changes when a process is completed.

In my HomeViewModel.kt I have:

@HiltViewModel
class HomeViewModel
@Inject
constructor(
    private val storageRepository: StorageRepository,
    private val accountRepository: AccountRepository,
) : ViewModel() {
// First state of isLoading is true
var uiState = mutableStateOf(HomeUiState())

...

fun addListener() {
    viewModelScope.launch {
        storageRepository.addListener(
            accountRepository.getUserId(),
            ::onDocumentEvent,
            onComplete = { 
                uiState.value = uiState.value.copy(isLoading = false) 
            },
            onError = { 
                error -> onAddListenerFailure(error) 
            }
        )
    }
}

And I want to write the test:

Given homeViewModel.addListener()

When storageRepository.addListener(...) completes

Then uiState.isLoading is false

I've been searching for some time now and I have found some people referring to using captors from mockito but nothing that applies to my case.

This is what I have now

@OptIn(ExperimentalCoroutinesApi::class)
internal class HomeViewModelTest {
  // mock repositories
  @Mock lateinit var storageRepository: StorageRepository
  @Mock lateinit var accountRepository: AccountRepository
  @Mock lateinit var logRepository: LogRepository

  // set dispatcher to be able to run tests
  private val dispatcher = StandardTestDispatcher()

  lateinit var callbackCaptor: KArgumentCaptor<() -> Unit>

  @Before
  fun setUp() {
    MockitoAnnotations.openMocks(this)
    Dispatchers.setMain(dispatcher)
  }

  @After
  fun tearDown() {
    Dispatchers.resetMain()
  }

  @Test
  fun `loading state is true when viewModel is created`() {
    val homeViewModel = HomeViewModel(storageRepository, accountRepository, logRepository)
    assertTrue(homeViewModel.uiState.value.isLoading)
  }

  @Test
  fun `loading state is false when listener is added successfully`() {
    val homeViewModel = HomeViewModel(storageRepository, accountRepository, logRepository)
    callbackCaptor = argumentCaptor()

    whenever(
        storageRepository.addListener(
          anyString(),
          anyOrNull(),
          callbackCaptor.capture(),
          anyOrNull()
        )
      )
      .thenAnswer { callbackCaptor.firstValue.invoke() }

    homeViewModel.addListener()

    // wait for mutable state to update
    dispatcher.scheduler.advanceUntilIdle()
    assertFalse(homeViewModel.uiState.value.isLoading)
  }
}

Of course, I'm open to hearing solutions using something else than captors.

Answer 1

I think you are not initialising the captor, try following

@Test
fun `loading state is false when listener completes its process`() {
    val homeViewModel = HomeViewModel(storageRepository, accountRepository, logRepository)

val callbackCaptor = argumentCaptor<() -> Unit>() //used kotlin mockito

    whenever(storageRepository.addListener(anyString(), any(), callbackCaptor.capture(), any()))
        .thenAnswer { callbackCaptor.firstValue.invoke() } 

    homeViewModel.addListener()

    // wait for mutable state to update
    dispatcher.scheduler.advanceUntilIdle()

    assertFalse(homeViewModel.uiState.value.isLoading)
}