Develop Reference

kotlinx.coroutines.test the latest API usage

I am working on a test case for ViewModel classes with the recent coroutines-test API and it doesn't work as expected.
#Test
fun `when balanceOf() is called with existing parameter model state is updated with correct value`() = runTest {
Dispatchers.setMain(StandardTestDispatcher())
fakeWalletRepository.setPositiveBalanceOfResponse()
assertThat("Model balance is not default", subj.uiState.value.wallet.getBalance().toInt() == 0)
assertThat("Errors queue is not empty", subj.uiState.value.errors.isEmpty())
assertThat("State is not default", subj.uiState.value.status == Status.NONE)
subj.balanceOf("0x6f1d841afce211dAead45e6109895c20f8ee92f0")
advanceUntilIdle()
assertThat("Model balance is not updated with correct value", subj.uiState.value.wallet.getBalance().toLong() == 42L)
assertThat("Errors queue is not empty", subj.uiState.value.errors.isEmpty())
assertThat("State is not set as BALANCE", subj.uiState.value.status == Status.BALANCE)
}
he issue is not working stably - usually it fails, under debugger usually it passes.
Based on my understanding StandartTestDispatcher shouldn't run coroutines until advanceUntilIdle call when UnconfinedTestDispatcher run them immediately. advanceUntilIdle should wait until all coroutines are finished, but it seems there is a race condition in the next assertThat() call which causes ambiguity in the behaviour of my test case.
advanceUntilIdle should guarantee all coroutines end their work. Does it mean race condition occurs somewhere under .collect{} or state.update {} calls? (In my understanding advanceUntilIdle should wait end of their execution too)
fun balanceOf(owner: String) {
logger.d("[start] balanceOf()")
viewModelScope.launch {
repository.balanceOf(owner)
.flowOn(Dispatchers.IO)
.collect { value ->
logger.d("collect get balance result")
processBalanceOfResponse(value)
}
}
logger.d("[end] balanceOf()")
}
state.update {
it.wallet.setBalance(value.data)
it.copy(wallet = it.wallet, status = Status.BALANCE)
}

From what i see the balanceOf() is executed on the IO dispatcher and you collect in the viewModelScope (which is the Main.Immediate dispatcher). The IO dispatcher is not overridden in your test and this is what causes the unpredictability of your test.
As there’s currently no way to override the IO dispatcher like with setMain, you can add the ability to override the background dispatcher in your ViewModel by adding a default argument, for example :
ViewModel(private val backgroundDispatcher: CoroutineDispatcher = Dispatchers.IO)
And replace it in your code :
fun balanceOf(owner: String) {
logger.d("[start] balanceOf()")
viewModelScope.launch {
repository.balanceOf(owner)
.flowOn(backgroundDispatcher)
.collect { value ->
logger.d("collect get balance result")
processBalanceOfResponse(value)
}
}
logger.d("[end] balanceOf()")
}
Then in your test you instantiate the ViewModel with the standard test dispatcher and it should work. You can check this page to understand the issue : https://developer.android.com/kotlin/coroutines/test#injecting-test-dispatchers

Unit Test for RxJava and Retrofit

I have This method that calls a Rest API and returns the result as an Observable (Single):
fun resetPassword(email: String): Single<ResetPassword> {
return Single.create { emitter ->
val subscription = mApiInterfacePanda.resetPassword(email)
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(Schedulers.io())
.subscribe({ resetPasswordResponse ->
when(resetPasswordResponse.code()) {
200 -> {
resetPasswordResponse?.body()?.let { resetPassword ->
emitter.onSuccess(resetPassword)
}
}
else -> emitter.onError(Exception("Server Error"))
}
}, { throwable ->
emitter.onError(throwable)
})
mCompositeDisposable.add(subscription)
}
}
Unit Test:
#Test
fun resetPassword_200() {
val response = Response.success(200, sMockResetPasswordResponse)
Mockito.`when`(mApiInterfacePanda.resetPassword(Mockito.anyString()))
.thenReturn(Single.just(response))
mTokenRepository.resetPassword(MOCK_EMAIL)
val observer = mApiInterfacePanda.resetPassword(MOCK_EMAIL)
val testObserver = TestObserver.create<Response<ResetPassword>>()
observer.subscribe(testObserver)
testObserver.assertSubscribed()
testObserver.awaitCount(1)
testObserver.assertComplete()
testObserver.assertResult(response)
}
My Problem is only this line gets covered and the other lines won't run and that has a lot of impact on my total test coverage:
return Single.create { emitter ->

There's more than one thing going on here if I'm not mistaken. Let's take it in parts.
First, your "internal" observer:
mApiInterfacePanda.resetPassword(email)
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(Schedulers.io())
.subscribe({ resetPasswordResponse -> ... })
Is observing on the android main thread and executing on a background thread. To the best of my knowledge, in most cases, the test thread will end before your mApiInterfacePanda .resetPassword has a chance to finish and run. You didn't really post the test setup, so I'm not sure if this is an actual issue, but in any case it's worth mentioning. Here's 2 ways to fix this:
RxJavaPlugins and RxAndroidPlugins
RxJava already provides a way to change the schedulers that are provided. An example is RxAndroidPlugins.setMainThreadSchedulerHandler. Here's how it could help:
#Before
fun setUp() {
RxAndroidPlugins.setInitMainThreadSchedulerHandler { Schedulers.trampoline() }
RxJavaPlugins.setInitIoSchedulerHandler { Schedulers.trampoline() }
}
The above methods make sure that everywhere you use the main thread scheduler and the io scheduler, it'll instead return the trampoline scheduler. This is a scheduler that guarantees that the code is executed in the same thread that was executing previously. In other words, it'll make sure you run it on the unit test main thread.
You will have to undo these:
#After
fun tearDown() {
RxAndroidPlugins.reset()
RxJavaPlugins.reset()
}
You can also change other schedulers.
Inject the schedulers
You can use kotlin's default arguments to help out with injecting schedulers:
fun resetPassword(
email: String,
obsScheduler: Scheduler = AndroidSchedulers.mainThread(),
subScheduler: Scheduler = Schedulers.io()
): Single<ResetPassword> {
return Single.create { emitter ->
val subscription = mApiInterfacePanda.resetPassword(email)
.observeOn(obsScheduler)
.subscribeOn(subScheduler)
.subscribe({ resetPasswordResponse ->
when(resetPasswordResponse.code()) {
200 -> {
resetPasswordResponse?.body()?.let { resetPassword ->
emitter.onSuccess(resetPassword)
}
}
else -> emitter.onError(Exception("Server Error"))
}
}, { throwable ->
emitter.onError(throwable)
})
mCompositeDisposable.add(subscription)
}
}
At test time you can just call it like resetPassword("foo#bar.com", Schedulers.trampoline(), Schedulers.trampoline() and for the application just pass in the email.
The other thing I see here is maybe not related to the problem, but I think it's still good to know. First, you're creating a single, but you don't need to do this.
Single.create is usually used when you don't have reactive code. However, mApiInterfacePanda.resetPassword(email) already returns a reactive component and although I'm not sure, let's just assume it's a single. If not, it should be fairly simple to convert it to something else.
You're also holding on to a disposable, which from what I can tell shouldn't be necessary.
Lastly, you're using retrofit according to your tags so you don't need to make the call return a raw response unless extremely necessary. This is true because retrofit checks the status code for you and will deliver the errors inside onError with an http exception. This is the Rx way of handling the errors.
With all this in mind, I'd rewrite the entire method like this:
fun resetPassword(email: String) = mApiInterfacePanda.resetPassword(email)
(note that resetPassword must not return a raw response, but Single<ResetPassword>
It actually shouldn't need anything else. Retrofit will make sure things end up in either onSuccess or onError. You don't need to subscribe to the result of the api here and handle disposables - let whoever is calling this code handle it.
You may also notice that if this is the case, then the solution for the schedulers is not needed. I guess this is true in this case, just remember some operators operate in some default schedulers and you may need to override them in some cases.
So how would I test the above method?
Personally I'd just check if the method calls the api with the right parameters:
#Test
fun resetPassword() {
mTokenRepository.resetPassword(MOCK_EMAIL)
verify(mApiInterfacePanda).resetPassword(MOCK_EMAIL)
}
I don't think there's much more needed here. There's no more logic I can see in the rewritten method.

Rx disposable not being created on time in unit tests

I'm having trouble with testing the manual manipulation of disposables inside my class being tested. I have a itemsProcessed map that keeps track of the different disposables that are created, the reason is that some disposables I need to be able to dispose on demand, and others I just need to know they exist.
My class runs fine and everything works as expected, but in my tests, I noticed that the disposables that I make aren't being inserted into my map until what would be the async code is already completed.
I'm not sure if it has anything to do with the fact that I'm using
RxJavaPlugins.setIoSchedulerHandler { Schedulers.trampoline() }
RxAndroidPlugins.setInitMainThreadSchedulerHandler { Schedulers.trampoline() }
Here are the relevant methods I'm testing, the myRepo.processItem() call is on a background thread
private fun processItem(item: Item) {
itemsProcessed[item] = myRepo.processItem(item)
.doOnComplete {
safelyDelete(item)
itemsProcessed.remove(item)
}
.doOnError {
itemsProcessed.remove(item)
}
.subscribe({}, {})
}
private fun cleanOldItems() {
itemList.forEach {
if (!itemsProcessed[item].exist())
safelyDelete(it)
}
}
myRepo has a processor called itemProcessor which calls the method above, my test is as follows
#Test
fun doNotDeleteItemsBeingProcessed() {
`when`(itemProcessor.processItem(any()))
.thenAnswer {
//from my understanding of disposables, the disposable should have been made in my real class and should have been inserted into the map at this point
trigger cleanOldItems
Completable.timer(5000, TimeUnit.MILLISECONDS)
}
repo.triggerProcessItems()
Assert.assertTrue(itemList.contains(item))
}
It seems like when I run the test, itemsProcessed map in my class is empty until the last assert line in my test is reached. When I added in doOnSubscribe, I noticed that doOnSubscribe was also called at the very end, what's causing this behaviour?

What does trigger cleanOldItems do? Assuming this is a synchronous call, then it'll call your cleaning function before it returns any disposable to store in your map. Instead, you should have
#Test
fun doNotDeleteItemsBeingProcessed() {
`when`(itemProcessor.processItem(any()))
.thenAnswer {
//from my understanding of disposables, the disposable should have been made in my real class and should have been inserted into the map at this point
Completable.timer(5000, TimeUnit.MILLISECONDS)
}
repo.triggerProcessItems()
repo.triggerCleanOldItems()
Assert.assertTrue(itemList.contains(item))
}
Also bear in mind that Completable.timer call uses computation scheduler internally, so unless you explicitly provide a scheduler to it (as in Completable.timer(5000, TimeUnit.MILLISECONDS, Schedulers.trampoline()) or override setComputationSchedulerHandler your subscription will be triggered on a different thread.

RxJava unit testing - Observable not emitting events in tests

I'm testing a view model which has the following definition:
class PostViewModel(private val postApi: PostApi): ViewModel() {
private val _post: PublishSubject<Post> = PublishSubject.create()
val postAuthor: Observable<String> = _post.map { it.author }
fun refresh(): Completable {
return postApi.getPost() // returns Single<Post>
.doOnSuccess {
_post.onNext(it)
}
.ignoreElement()
}
}
}
My fragment then displays the post author by subscribing to viewModel.postAuthor in its onActivityCreated and calling and subscribing to refresh() whenever the user wants an updated post and everything is fine and dandy.
The issue I'm running into is trying to verify this behaviour in a unit test: specifically, I am unable to get postAuthor to emit an event in my testing environment.
My test is defined as follows:
#Test
fun `When view model is successfully refreshed, display postAuthor`() {
val post = Post(...)
whenever(mockPostApi.getPost().thenReturn(Single.just(post))
viewModel.refresh()
.andThen(viewModel.postAuthor)
.test()
.assertValue { it == "George Orwell" }
}
The test fails due to no values or errors being emitted, even though I can verify through the debugger that the mock does in-fact return the Post as expected. Is there something obvious that I'm missing, or am I completely wrong in my testing approach?

viewModel.postAuthor is a hot-observable. It emits value when you call _post.onNext(it).
Unlike a cold-observable, the late subscribers cannot receive the values that got emitted before they subscribe.
So in your case I think the viewModel.postAuthor is subscribed after you call viewModel.refresh(), so it cannot receive the value.

The observable could be emitting on a different thread so that's why it's empty when the test is checking the values/errors.
You could try forcing your observable to emit on the same thread. Depending on which scheduler you're using, it'd be something like:
RxJavaPlugins.setIoSchedulerHandler { Schedulers.trampoline() }

Unit testing RxJava + Retrofit call inside the method

The method I want to test contains of two calls to the retrofit service:
internal fun poll(): Completable {
return presenceService.askForFrequency(true).toObservable()
.flatMap { it -> Observable.interval(it.frequency, TimeUnit.SECONDS, Schedulers.io()) }
.flatMapCompletable { _ -> presenceService.sendHeartbeat() }
.subscribeOn(Schedulers.io())
.retry()
}
The presenceService is injected in the class, so I provide the mocked one for the test:
val frequency = PublishSubject.create<Presence>()
val heartbeat = PublishSubject.create<Unit>()
val mockPresenceService = mock<PresenceService> {
on { askForFrequency(any()) } doReturn frequency
on { sendHeartbeat() } doReturn heartbeat
}
The test, that checks that askForFrequency method is called works correctly, but test that checks that the polling request is sent never works:
#Test
fun presenceService_sentHeartbeat() {
RxJavaPlugins.setIoSchedulerHandler { scheduler }
frequency.onNext(Presence(1)) //polls with 1s interval
heartbeat.onNext(Unit)
presenceMaintainer.onActivityResumed(any())
scheduler.advanceTimeBy(2, TimeUnit.SECONDS)
verify(mockPresenceService).askForFrequency(true) //works correctly
verify(mockPresenceService).sendHeartbeat() //never works
}
The logs from the unit test run are:
Wanted but not invoked:
presenceService.sendHeartbeat();
However, there was exactly 1 interaction with this mock:
presenceService.askForFrequency(true);
The question is: how to test that the second method (sendHeartbeat) is also called (possibly several times)?
Meanwhile I found out that the problem lies in the second flatmap, because the test for this method works correctly (verifies that method was called 60 times):
internal fun pollTest(): Observable<Presence> {
return Observable.interval(1, TimeUnit.SECONDS, Schedulers.io())
.subscribeOn(Schedulers.io())
.flatMap { it -> presenceService.askForFrequency(true).toObservable() }
}
#Test
fun presenceService_sentHeartbeat() {
frequency.onNext(Presence(1))
val result = arrayListOf<Unit>()
presenceMaintainer.pollTest().subscribe({ t -> result.add(Unit) })
Thread.sleep(60*1000)
println(result.size)
verify(mockPresenceService, Times(60)).askForFrequency(true)
}
But when I change the order of the calls to askForFrequency -> map to interval -> map each tick to poll call, test stops working and mock is called only once.

By default, Observable.interval() runs on the computation scheduler, and not the io scheduler. That means, that the 2 second wait will be run in real time, so your test will finish 2 seconds before the call to sendHeartBeat().