Testing simple Loading+fetch flow with Coroutines as Android Instrumented tests with StandardTestDispatcher

Question

I want to test the following very common usecase as an Instrumented Test in Android:

When clicking a button a fetch() function is called in my ViewModel
This function tells the view to show a loading-overlay
It executes a fetch in a coroutine
After the result is fetched it lets the view know to display the result

Here is the function in my Viewmodel:

fun fetch() {
    _loading.value = true //loading is shown
    viewModelScope.launch {
        val results = fetchUseCase() //suspend function
        _result.postValue(results)
        _loading.postValue(false) //loading is not displayed
    }
}

Here is the test which works according to this CodeLab https://developer.android.com/codelabs/advanced-android-kotlin-training-testing-survey#4:

@HiltAndroidTest
@UninstallModules(CoroutinesDispatcherModule::class)
@RunWith(AndroidJUnit4::class)
class ExampleInstrumentedTestJunit4Deprecated {

@get:Rule
var hiltRule = HiltAndroidRule(this)

@ExperimentalCoroutinesApi
@get:Rule
var mainCoroutineRule = MainCoroutineRule()

@Before
fun setup() {
    ActivityScenario.launch(HomeScreenActivity::class.java)
}

@ExperimentalCoroutinesApi
@Test
fun fetchTest() {

    //pausing the long running tasks
    mainCoroutineRule.pauseDispatcher()

    //When clicking the button
    onView(withId(R.id.load_measurement_button)).perform(click())

    //loading is shown
    onView(withId(R.id.loading_overlay))
        .check(matches(withEffectiveVisibility(ViewMatchers.Visibility.VISIBLE)))

    //continue fetch
    mainCoroutineRule.resumeDispatcher()

    // loading is not shown anymore and the result is there
    onView(withId(R.id.loading_overlay))
        .check(matches(withEffectiveVisibility(ViewMatchers.Visibility.GONE)))
    onView(withId(R.id.message))
        .check(matches(withText("0")))
}
}

Unfortunately "pauseDispatcher()" and "resumeDispatcher" are Deprecated. I tried to use the "StandardTestDispatcher" and "advanceUntilIdle()" but it does not work as expected. The coroutine is never resumed. How can this test be rewritten, such that it works:

Without deprecated function calls
Without changing the productive code ?

Testing simple Loading+fetch flow with Coroutines as Android Instrumented tests with StandardTestDispatcher

0 Answers0