Test a view model with livedata, coroutines (Kotlin) - kotlin

Question

I've been trying to test my view model for several days without success.
This is my view model :
class AdvertViewModel : ViewModel() {
private val parentJob = Job()
private val coroutineContext: CoroutineContext
get() = parentJob + Dispatchers.Default
private val scope = CoroutineScope(coroutineContext)
private val repository : AdvertRepository = AdvertRepository(ApiFactory.Apifactory.advertService)
val advertContactLiveData = MutableLiveData<String>()
fun fetchRequestContact(requestContact: RequestContact) {
scope.launch {
val advertContact = repository.requestContact(requestContact)
advertContactLiveData.postValue(advertContact)
}
}
}
This is my repository :
class AdvertRepository (private val api : AdvertService) : BaseRepository() {
suspend fun requestContact(requestContact: RequestContact) : String? {
val advertResponse = safeApiCall(
call = {api.requestContact(requestContact).await()},
errorMessage = "Error Request Contact"
)
return advertResponse
}
}
This is my view model test :
#RunWith(JUnit4::class)
class AdvertViewModelTest {
private val goodContact = RequestContact(...)
private lateinit var advertViewModel: AdvertViewModel
private var observer: Observer<String> = mock()
#get:Rule
var instantTaskExecutorRule = InstantTaskExecutorRule()
#Before
fun setUp() {
advertViewModel = AdvertViewModel()
advertViewModel.advertContactLiveData.observeForever(observer)
}
#Test
fun fetchRequestContact_goodResponse() {
advertViewModel.fetchRequestContact(goodContact)
val captor = ArgumentCaptor.forClass(String::class.java)
captor.run {
verify(observer, times(1)).onChanged(capture())
assertEquals("someValue", value)
}
}
}
The method mock() :
inline fun <reified T> mock(): T = Mockito.mock(T::class.java)
I got this error :
Wanted but not invoked: observer.onChanged();
-> at com.vizzit.AdvertViewModelTest.fetchRequestContact_goodResponse(AdvertViewModelTest.kt:52)
Actually, there were zero interactions with this mock.
I don't understand how to retrieve the result of my query.

Answer 1

You would need to write a OneTimeObserver to observe livedata from the ViewModel
class OneTimeObserver<T>(private val handler: (T) -> Unit) : Observer<T>, LifecycleOwner {
private val lifecycle = LifecycleRegistry(this)
init {
lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_RESUME)
}
override fun getLifecycle(): Lifecycle = lifecycle
override fun onChanged(t: T) {
handler(t)
lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_DESTROY)
}
}
After that you can write an extension function:
fun <T> LiveData<T>.observeOnce(onChangeHandler: (T) -> Unit) {
val observer = OneTimeObserver(handler = onChangeHandler)
observe(observer, observer)
}
Than you can check this ViewModel class class that I have from a project to check what's going on with your LiveData after you act (when) with invoking a method.
As for your error, it just says that the onChanged() method is not being called ever.