Hi guys, I am getting strange issue using `runTest` . I have a simple viewModel ```class LoadingView...

# coroutines

[KotlinLeaner]

Hi guys, I am getting strange issue using runTest . I have a simple viewModel

class LoadingViewModel(
    private val ioDispatcher: CoroutineDispatcher,
) : ViewModel() {

    var xyz by mutableStateOf(false)
    fun checkXyz() {
        viewModelScope.launch {
            delay(1000L)
            xyz = true
        }
    }
}

more code in 🧵

[KotlinLeaner]

@OptIn(ExperimentalCoroutinesApi::class)
class LoadingViewModelTest {

    private val subject by lazy {
        spyk(LoadingViewModel(UnconfinedTestDispatcher()))
    }

@Before
    fun setUp() {
        MockKAnnotations.init(this, relaxed = true)
    }

    @Test
    fun `xyz - when method called then should assign value on xyz`() = runTest {

        subject.checkXyz()
        verify {
            <http://subject.xyz|subject.xyz> = true
        }
    }
}

[KotlinLeaner]

I am using junit4 with kotlin 1.8.10

[KotlinLeaner]

Getting error

Verification failed: call 1 of 1: LoadingViewModel(#3).setXyz(eq(true))) was not called.

Calls to same mock:
1) LoadingViewModel(#3).checkXyz()
2) LoadingViewModel(#3).getTag(androidx.lifecycle.ViewModelCoroutineScope.JOB_KEY)
3) LoadingViewModel(#3).setTagIfAbsent(androidx.lifecycle.ViewModelCoroutineScope.JOB_KEY, androidx.lifecycle.CloseableCoroutineScope@2d5580f6)

[KotlinLeaner]

I checked and If removed delay it working fine.

[Joffrey]

Well if you have a delay, you're not setting xyz immediately, so why do you think you can immediately verify that it has been set?

[ephemient]

also the delay in viewModelScope doesn't use the TestCoroutineScheduler, so this isn't testable anyway

[Joffrey]

Even if it were using the test scheduler, the test doesn't wait for this delay (even virtually)

[ephemient]

yep. advanceTimeBy can move virtual time to allow you to observe the post-delay effects, but not in this case because viewModelScope is totally separate

[Joffrey]

Yes, what I meant is that the test doesn't even attempt to do it, but yeah it wouldn't work anyway. Not only the subject doesn't pass the given test dispatcher to the launch internally, but also it's given a different test dispatcher than the one from the runTest call, so I don't think it would work even if subject used its ioDispatcher property in the launch.

[KotlinLeaner]

Hi Joffrey why do you think you can immediately verify that it has been set? I am just testing the function and see in the document delay can we skip by using runTest.

[KotlinLeaner]

I tried to use ioDispatcher inside my viewModelScope but still I am getting error.

fun checkXyz() {
     viewModelScope.launch(ioDispatcher) {
        delay(1000L)
        xyz = true
     }
 }

what else I need to add in test?