Issue
I have a function in ViewModel with 2 states, first state is always LOADING, second state depends on result of api or db interactions.
This is the function
fun getPostWithSuspend() {
myCoroutineScope.launch {
// Set current state to LOADING
_postStateWithSuspend.value = ViewState(LOADING)
val result = postsUseCase.getPosts()
// Check and assign result to UI
val resultViewState = if (result.status == SUCCESS) {
ViewState(SUCCESS, data = result.data?.get(0)?.title)
} else {
ViewState(ERROR, error = result.error)
}
_postStateWithSuspend.value = resultViewState
}
}
And no error, test works fine for checking final result of ERROR or SUCCESS
@Test
fun `Given DataResult Error returned from useCase, should result error`() =
testCoroutineRule.runBlockingTest {
// GIVEN
coEvery {
useCase.getPosts()
} returns DataResult.Error(Exception("Network error occurred."))
// WHEN
viewModel.getPostWithSuspend()
// THEN
val expected = viewModel.postStateWithSuspend.getOrAwaitMultipleValues(dataCount = 2)
// Truth.assertThat("Network error occurred.").isEqualTo(expected?.error?.message)
// Truth.assertThat(expected?.error).isInstanceOf(Exception::class.java)
coVerify(atMost = 1) { useCase.getPosts() }
}
But i couldn't find a way to test whether LOADING
state has occurred or not, so i modified existing extension function to
fun <T> LiveData<T>.getOrAwaitMultipleValues(
time: Long = 2,
dataCount: Int = 1,
timeUnit: TimeUnit = TimeUnit.SECONDS,
afterObserve: () -> Unit = {}
): List<T?> {
val data = mutableListOf<T?>()
val latch = CountDownLatch(dataCount)
val observer = object : Observer<T> {
override fun onChanged(o: T?) {
data.add(o)
latch.countDown()
[email protected](this)
}
}
this.observeForever(observer)
afterObserve.invoke()
// Don't wait indefinitely if the LiveData is not set.
if (!latch.await(time, timeUnit)) {
this.removeObserver(observer)
throw TimeoutException("LiveData value was never set.")
}
@Suppress("UNCHECKED_CAST")
return data.toList()
}
To add data to a list when LiveData changes and store states in that list but
it never returns LOADING state because it happens before observe starts. Is there a way to test multiple values of LiveData
?
Solution
Using mockk you can capture the values and store it in the list, then you check the values by order.
//create mockk object
val observer = mockk<Observer<AnyObject>>()
//create slot
val slot = slot<AnyObject>()
//create list to store values
val list = arrayListOf<AnyObject>()
//start observing
viewModel.postStateWithSuspend.observeForever(observer)
//capture value on every call
every { observer.onChanged(capture(slot)) } answers {
//store captured value
list.add(slot.captured)
}
viewModel.getPostWithSuspend()
//assert your values here
Answered By - iamanbansal