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Test a usecase with multiple coroutines (withContext and suspend) does not fail where expected

I created an instrumental test for a use case which has two coroutines, before fetching data and after. I run a test on the usecase but the test passes before the suspend function is done.
Usecase:
class FetchAllUseCase : Observable<FetchAllUseCase.Listener>() {
interface Listener {
fun onFetched(obj: List<Obj>)
}
fun fetchObjs() {
GlobalScope.launch(Dispatchers.IO) {
withContext(NonCancellable) {
val objs: List<Obj> = getObjs()
notify(objs)
}
}
}
private suspend fun notify(objs: List<Objs>) {
withContext(Dispatchers.Main) {
for(listener in listeners){
listener.onFetched(objs)
}
}
}
private fun getObjss(): List<Obj> {
/// fetch objects functionality
}
Test:
class FetchAllUseCase Test: FetchAllUseCase .Listener {
private lateinit var fetchAllUseCase: FetchAllUseCase
#Before
fun setUp() {
fetchAllUseCase = FetchAllUseCase()
fetchAllUseCase.registerListener(this)
}
#After
fun tearDown() {
fetchAllUseCase.unregisterListener(this)
}
#ExperimentalCoroutinesApi
#Test
fun fetchObjss()= runBlocking{
fetchAllUseCase.fetchObjs()
}
override fun onFetched(objs: List<Objs>) {
fail() //does not fail the test
}
}
Test already passes before onFetched() is called.
fail() or any other assertEquals that should fail the test does not affect the test result.
If I run the test on the MainActivity , adding:
#Rule
#JvmField
val mMainActivityTestRule = ActivityTestRule(MainActivity::class.java)
I will get a message "Process crashed" , but the test already passed.
If I remove both coroutines, the test works as expected, i.e fails.
I tried runBlocking, runBlockingTest, TestCoroutineDispatcher
None solved the issue so far

Add Dispatchers as Dependencies
class FetchAllUseCase(
private val mainDispatcher : CoroutineDispatcher = Dispatchers.Main,
private val ioDispatcher : CoroutineDispatcher = Dispatchers.IO,
) : Observable<FetchAllUseCase.Listener>() {
interface Listener {
fun onFetched(obj: List<Obj>)
}
fun fetchObjs() {
GlobalScope.launch(ioDispatcher) {
withContext(NonCancellable) {
val objs: List<Obj> = getObjs()
notify(objs)
}
}
}
private suspend fun notify(objs: List<Objs>) {
withContext(mainDispatcher) {
for(listener in listeners){
listener.onFetched(objs)
}
}
}
private fun getObjss(): List<Obj> {
/// fetch objects functionality
}
Testing, Inject The TestCoroutineDispatcher and use runBlockingTest
class FetchAllUseCase Test: FetchAllUseCase .Listener {
private lateinit var fetchAllUseCase: FetchAllUseCase
private val testDispatcher = TestCoroutineDispatcher()
#Before
fun setUp() {
fetchAllUseCase = FetchAllUseCase(testDispatcher,testDispatcher)
fetchAllUseCase.registerListener(this)
}
#After
fun tearDown() {
fetchAllUseCase.unregisterListener(this)
}
#ExperimentalCoroutinesApi
#Test
fun fetchObjss()= runBlockingTest{
fetchAllUseCase.fetchObjs()
}
override fun onFetched(objs: List<Objs>) {
fail() //does not fail the test
}
If This Didn't work checkout this link Kotlin Coroutines in Android — Unit Test

ViewModel unit tests fail when run together but pass when run individually

I am testing a suspended method from my ViewModel that triggers LiveData to emit an object when coroutine is completed. When
I run each of those tests individually they pass, when I run them together always the first test fails. Surprisingly, when I run them in debug and I put break points at assertValue to check what the vaule is, both of the test pass. My guess is that the problem is with the state of LiveData or the whole PaymentViewModel. What am I doing wrong?
class PaymentViewModelTest : KoinTest {
private val paymentViewModel : PaymentViewModel by inject()
#get:Rule
val instantTaskExecutorRule = InstantTaskExecutorRule()
private val mainThreadSurrogate = newSingleThreadContext("UI thread")
#Before
fun setup(){
Dispatchers.setMain(mainThreadSurrogate)
val modules = KoinModule()
startKoin {
androidContext(mock(Application::class.java))
modules(listOf(
modules.repositoryModule,
modules.businessModule,
modules.utilsModule)
)
}
declareMock<AnalyticsHelper>()
declareMock<Printer>()
}
#After
fun after(){
stopKoin()
Dispatchers.resetMain()
}
#Test
fun successfully_initializes_payment_flow() {
declareMock<PaymentRepository> {
runBlockingTest {
given(initPayment())
.willAnswer { InitPaymentResponse(0, PaymentStatus.INITIALIZED, 0) }
}
}
paymentViewModel.initPayment(BigDecimal(0))
paymentViewModel.paymentStatus.test()
.awaitValue()
.assertValue { value -> value.getContentIfNotHandled()?.data == PaymentStatus.INITIALIZED }
}
#Test
fun fails_to_initialize_payment_flow() {
declareMock<PaymentRepository> {
runBlockingTest {
given(initPayment())
.willThrow(MockitoKotlinException("", ConnectException()))
}
}
paymentViewModel.initPayment(BigDecimal(0))
paymentViewModel.paymentStatus.test()
.awaitValue()
.assertValue { value -> value.getContentIfNotHandled()?.status == ApiResponseStatus.ERROR}
}
}
Here is the method that I am testing:
fun initPayment(price: BigDecimal) {
paymentStatus.postValue(Event(ApiResponse.loading()))
viewModelScope.launch {
runCatching {
repository.initPayment()
}.onSuccess {
paymentSession = PaymentSession(it.paymentId)
paymentSession.price = price
postPaymentStatus(it.status)
}.onFailure {
postApiError(it)
}
}
}
private fun postPaymentStatus(status: PaymentStatus) =
paymentStatus.postValue(Event(ApiResponse.success(status)))

This might not be a complete answer because there is so much in your question. Start by trying to use a CoroutineTestRule:
#ExperimentalCoroutinesApi
class CoroutineTestRule(
private val testDispatcher: TestCoroutineDispatcher = TestCoroutineDispatcher()
) : TestWatcher() {
override fun starting(description: Description?) {
Dispatchers.setMain(testDispatcher)
}
override fun finished(description: Description?) {
Dispatchers.resetMain()
testDispatcher.cleanupTestCoroutines()
}
}
Your test will be something like:
class PaymentViewModelTest : KoinTest {
private val paymentViewModel : PaymentViewModel by inject()
#get:Rule
val coroutineTestRule = CoroutineTestRule()
#Before
fun setup(){
startKoin {
androidContext(mock(Application::class.java))
modules(
modules.repositoryModule,
modules.businessModule,
modules.utilsModule
)
}
declareMock<AnalyticsHelper>()
declareMock<Printer>()
}
#After
fun after(){
stopKoin()
}
// Other methods are the same.
}
You can use an AutoCloseKoinTest to remove that after() method.
You say that the test is passing when you run it isolated, so maybe this is enough. But there is more to dig into if this doesn't work. For example, I find it strange that you use runBlockingTest inside a mock and the assert is outside that block. Usually I would use MockK to mock suspending functions and test and assert any of them inside a runBlockingTest.

Test LiveData and Coroutines using MockK

I have this view model:
class MyViewModel(private val myUseCase: MyUseCase) : ViewModel() {
val stateLiveData = MutableLiveData(State.IDLE)
fun onButtonPressed() {
viewModelScope.launch {
stateLiveData.value = State.LOADING
myUseCase.loadStuff() // Suspend
stateLiveData.value = State.SUCCESS
}
}
}
I'd like to write a test that checks whether the state is really LOADING while myUseCase.loadStuff() is running. I'm using MockK for that. Here's the test class:
#ExperimentalCoroutinesApi
class MyViewModelTest {
#get:Rule
val rule = InstantTaskExecutorRule()
private lateinit var myUseCase: MyUseCase
private lateinit var myViewModel: MyViewModel
#Before
fun setup() {
myUseCase = mockkClass(MyUseCase::class)
myViewModel = MyViewModel(myUseCase)
}
#Test
fun `button click should put screen into loading state`() = runBlockingTest {
coEvery { myUseCase.loadStuff() } coAnswers { delay(2000) }
myViewModel.onButtonPressed()
advanceTimeBy(1000)
val state = myViewModel.stateLiveData.value
assertEquals(State.LOADING, state)
}
}
It fails:
java.lang.AssertionError:
Expected :LOADING
Actual :IDLE
How can I fix this?

I only needed to make a few changes in the test class to make it pass:
#ExperimentalCoroutinesApi
class MyViewModelTest {
#get:Rule
val rule = InstantTaskExecutorRule()
private val dispatcher = TestCoroutineDispatcher()
private lateinit var myUseCase: MyUseCase
private lateinit var myViewModel: MyViewModel
#Before
fun setup() {
Dispatchers.setMain(dispatcher)
myUseCase = mockkClass(MyUseCase::class)
myViewModel = MyViewModel(myUseCase)
}
#After
fun cleanup() {
Dispatchers.resetMain()
}
#Test
fun `button click should put screen into loading state`() {
dispatcher.runBlockingTest {
coEvery { myUseCase.loadStuff() } coAnswers { delay(2000) }
myViewModel.onButtonPressed()
// This isn't even needed.
advanceTimeBy(1000)
val state = myViewModel.stateLiveData.value
assertEquals(State.LOADING, state)
}
}
}
No changes needed in the view model at all! :D
Thanks Kiskae for such helpful advice!

Your problem lies in the fact that viewModelScope dispatches to Dispatcher.MAIN, not the testing dispatcher created by runBlockingTest. This means that even with the call to advanceTimeBy the code does not get executed.
You can solve the issue by using Dispatcher.setMain(..) to replace the MAIN dispatcher with your test dispatcher. This will require managing the dispatcher yourself instead of relying on the stand-alone runBlockingTest.

Unit test a ViewModel method that uses ViewModelScope.launch to call a suspend function with delay

In my ViewModel I have an onTextChanged method that is called via databinding on an EditText. In there I use viewModelScope.launch{} to start a suspend function. In that function I delay for 500ms. Now how do I test the onTextChanged method? Everything I tried always results in the test finishing before the delay is done. I tried with runBlockingTest, TestCoroutineDispatcher and runBlocking.
The textwatcher:
override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {
searchJob = if (searchJob?.isActive == true) {
searchJob?.cancel()
viewModelScope.launch { search(s.toString()) }
} else {
viewModelScope.launch { search(s.toString()) }
}
}
The search method:
private suspend fun search(query: String) {
delay(500)
searchUseCase(SearchParams(query)).fold({
}, {
})
}
The test:
#Test
fun `Search is fired after 500ms when text is changed`() = runBlockingTest {
val viewModel = ViewModel(useCase)
viewModel.onTextChanged("test", 0, 0, 0)
//TODO assert time was 500ms or more
//This fails
coVerify(exactly = 1) { useCase.invoke(any()) }
}

What's recommended by google, is that you should somehow inject CoroutineDispatcher to your view model, so that you can change it during tests.
class MainViewModel(
private val dispatcher: CoroutineDispatcher = Dispatchers.Default
) : ViewModel() {
private var _userData: MutableLiveData<Any> = MutableLiveData<Any>()
val userData: LiveData<Any> = _userData
fun savedDelayed() = viewModelScope.launch {
delay(1000)
saveSessionData()
}
suspend fun saveSessionData() {
viewModelScope.launch(dispatcher) {
_userData.value = "some_user_data"
}
}
}
#ExperimentalCoroutinesApi
class MainViewModelTest {
private val testDispatcher = TestCoroutineDispatcher()
#ExperimentalCoroutinesApi
#get:Rule
var mainCoroutineRule = MainCoroutineRule()
#get:Rule
var instantExecutorRule = InstantTaskExecutorRule()
#Test
fun testsSaveSessionData() = runBlockingTest {
val mainViewModel = MainViewModel(testDispatcher)
mainViewModel.savedDelayed()
testDispatcher.advanceUntilIdle()
val userData = mainViewModel.userData.value
assertEquals("some_user_data", userData)
}
}
Code pasted from medium article, with modifications for your use case. Please read article for further explanation:
https://medium.com/swlh/unit-testing-with-kotlin-coroutines-the-android-way-19289838d257

Coroutines - unit testing viewModelScope.launch methods

I am writing unit tests for my viewModel, but having trouble executing the tests. The runBlocking { ... } block doesn't actually wait for the code inside to finish, which is surprising to me.
The test fails because result is null. Why doesn't runBlocking { ... } run the launch block inside the ViewModel in blocking fashion?
I know if I convert it to a async method that returns a Deferred object, then I can get the object by calling await(), or I can return a Job and call join(). But, I'd like to do this by leaving my ViewModel methods as void functions, is there a way to do this?
// MyViewModel.kt
class MyViewModel(application: Application) : AndroidViewModel(application) {
val logic = Logic()
val myLiveData = MutableLiveData<Result>()
fun doSomething() {
viewModelScope.launch(MyDispatchers.Background) {
System.out.println("Calling work")
val result = logic.doWork()
System.out.println("Got result")
myLiveData.postValue(result)
System.out.println("Posted result")
}
}
private class Logic {
suspend fun doWork(): Result? {
return suspendCoroutine { cont ->
Network.getResultAsync(object : Callback<Result> {
override fun onSuccess(result: Result) {
cont.resume(result)
}
override fun onError(error: Throwable) {
cont.resumeWithException(error)
}
})
}
}
}
// MyViewModelTest.kt
#RunWith(RobolectricTestRunner::class)
class MyViewModelTest {
lateinit var viewModel: MyViewModel
#get:Rule
val rule: TestRule = InstantTaskExecutorRule()
#Before
fun init() {
viewModel = MyViewModel(ApplicationProvider.getApplicationContext())
}
#Test
fun testSomething() {
runBlocking {
System.out.println("Called doSomething")
viewModel.doSomething()
}
System.out.println("Getting result value")
val result = viewModel.myLiveData.value
System.out.println("Result value : $result")
assertNotNull(result) // Fails here
}
}

What you need to do is wrap your launching of a coroutine into a block with given dispatcher.
var ui: CoroutineDispatcher = Dispatchers.Main
var io: CoroutineDispatcher = Dispatchers.IO
var background: CoroutineDispatcher = Dispatchers.Default
fun ViewModel.uiJob(block: suspend CoroutineScope.() -> Unit): Job {
return viewModelScope.launch(ui) {
block()
}
}
fun ViewModel.ioJob(block: suspend CoroutineScope.() -> Unit): Job {
return viewModelScope.launch(io) {
block()
}
}
fun ViewModel.backgroundJob(block: suspend CoroutineScope.() -> Unit): Job {
return viewModelScope.launch(background) {
block()
}
}
Notice ui, io and background at the top. Everything here is top-level + extension functions.
Then in viewModel you start your coroutine like this:
uiJob {
when (val result = fetchRubyContributorsUseCase.execute()) {
// ... handle result of suspend fun execute() here
}
And in test you need to call this method in #Before block:
#ExperimentalCoroutinesApi
private fun unconfinifyTestScope() {
ui = Dispatchers.Unconfined
io = Dispatchers.Unconfined
background = Dispatchers.Unconfined
}
(Which is much nicer to add to some base class like BaseViewModelTest)

As others mentioned, runblocking just blocks the coroutines launched in it's scope, it's separate from your viewModelScope.
What you could do is to inject your MyDispatchers.Background and set the mainDispatcher to use dispatchers.unconfined.

As #Gergely Hegedus mentions above, the CoroutineScope needs to be injected into the ViewModel. Using this strategy, the CoroutineScope is passed as an argument with a default null value for production. For unit tests the TestCoroutineScope will be used.
SomeUtils.kt
/**
* Configure CoroutineScope injection for production and testing.
*
* #receiver ViewModel provides viewModelScope for production
* #param coroutineScope null for production, injects TestCoroutineScope for unit tests
* #return CoroutineScope to launch coroutines on
*/
fun ViewModel.getViewModelScope(coroutineScope: CoroutineScope?) =
if (coroutineScope == null) this.viewModelScope
else coroutineScope
SomeViewModel.kt
class FeedViewModel(
private val coroutineScopeProvider: CoroutineScope? = null,
private val repository: FeedRepository
) : ViewModel() {
private val coroutineScope = getViewModelScope(coroutineScopeProvider)
fun getSomeData() {
repository.getSomeDataRequest().onEach {
// Some code here.
}.launchIn(coroutineScope)
}
}
SomeTest.kt
#ExperimentalCoroutinesApi
class FeedTest : BeforeAllCallback, AfterAllCallback {
private val testDispatcher = TestCoroutineDispatcher()
private val testScope = TestCoroutineScope(testDispatcher)
private val repository = mockkClass(FeedRepository::class)
private var loadNetworkIntent = MutableStateFlow<LoadNetworkIntent?>(null)
override fun beforeAll(context: ExtensionContext?) {
// Set Coroutine Dispatcher.
Dispatchers.setMain(testDispatcher)
}
override fun afterAll(context: ExtensionContext?) {
Dispatchers.resetMain()
// Reset Coroutine Dispatcher and Scope.
testDispatcher.cleanupTestCoroutines()
testScope.cleanupTestCoroutines()
}
#Test
fun topCafesPoc() = testDispatcher.runBlockingTest {
...
val viewModel = FeedViewModel(testScope, repository)
viewmodel.getSomeData()
...
}
}

I tried the top answer and worked, but I didn't want to go over all my launches and add a dispatcher reference to main or unconfined in my tests. So I ended up adding this code to my base testing class. I am defining my dispatcher as TestCoroutineDispatcher()
class InstantExecutorExtension : BeforeEachCallback, AfterEachCallback {
private val mainThreadDispatcher = TestCoroutineDispatcher()
override fun beforeEach(context: ExtensionContext?) {
ArchTaskExecutor.getInstance()
.setDelegate(object : TaskExecutor() {
override fun executeOnDiskIO(runnable: Runnable) = runnable.run()
override fun postToMainThread(runnable: Runnable) = runnable.run()
override fun isMainThread(): Boolean = true
})
Dispatchers.setMain(mainThreadDispatcher)
}
override fun afterEach(context: ExtensionContext?) {
ArchTaskExecutor.getInstance().setDelegate(null)
Dispatchers.resetMain()
}
}
in my base test class I have
#ExtendWith(MockitoExtension::class, InstantExecutorExtension::class)
#TestInstance(TestInstance.Lifecycle.PER_CLASS)
abstract class BaseTest {
#BeforeAll
private fun doOnBeforeAll() {
MockitoAnnotations.initMocks(this)
}
}

I did use the mockk framework that helps to mock the viewModelScope instance like below
https://mockk.io/
viewModel = mockk<MyViewModel>(relaxed = true)
every { viewModel.viewModelScope}.returns(CoroutineScope(Dispatchers.Main))

There are 3 steps that you need to follow.
Add dependency in gradle file.
testImplementation ("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.6.1")
{ exclude ("org.jetbrains.kotlinx:kotlinx-coroutines-debug") }
Create a Rule class MainCoroutineRule
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.test.StandardTestDispatcher
import kotlinx.coroutines.test.TestDispatcher
import kotlinx.coroutines.test.resetMain
import kotlinx.coroutines.test.setMain
import org.junit.rules.TestWatcher
import org.junit.runner.Description
#ExperimentalCoroutinesApi
class MainCoroutineRule(private val testDispatcher: TestDispatcher = StandardTestDispatcher()) :
TestWatcher() {
override fun starting(description: Description) {
super.starting(description)
Dispatchers.setMain(testDispatcher)
}
override fun finished(description: Description) {
super.finished(description)
Dispatchers.resetMain()
}
}
Modify your test class to use ExperimentalCoroutinesApi runTest and advanceUntilIdle()
#OptIn(ExperimentalCoroutinesApi::class) // New addition
internal class ConnectionsViewModelTest {
#ExperimentalCoroutinesApi
#get:Rule
var mainCoroutineRule = MainCoroutineRule() // New addition
...
#Test
fun test_abcd() {
runTest { // New addition
...
val viewModel = MyViewModel()
viewModel.foo()
advanceUntilIdle() // New addition
verify { mockObject.footlooseFunction() }
}
}
For explanation on why to do this you can always refer to the codelab https://developer.android.com/codelabs/advanced-android-kotlin-training-testing-survey#3

The problem you are having stems not from runBlocking, but rather from LiveData not propagating a value without an attached observer.
I have seen many ways of dealing with this, but the simplest is to just use observeForever and a CountDownLatch.
#Test
fun testSomething() {
runBlocking {
viewModel.doSomething()
}
val latch = CountDownLatch(1)
var result: String? = null
viewModel.myLiveData.observeForever {
result = it
latch.countDown()
}
latch.await(2, TimeUnit.SECONDS)
assertNotNull(result)
}
This pattern is quite common and you are likely to see many projects with some variation of it as a function/method in some test utility class/file, e.g.
#Throws(InterruptedException::class)
fun <T> LiveData<T>.getTestValue(): T? {
var value: T? = null
val latch = CountDownLatch(1)
val observer = Observer<T> {
value = it
latch.countDown()
}
latch.await(2, TimeUnit.SECONDS)
observeForever(observer)
removeObserver(observer)
return value
}
Which you can call like this:
val result = viewModel.myLiveData.getTestValue()
Other projects make it a part of their assertions library.
Here is a library someone wrote dedicated to LiveData testing.
You may also want to look into the Kotlin Coroutine CodeLab
Or the following projects:
https://github.com/googlesamples/android-sunflower
https://github.com/googlesamples/android-architecture-components

You don't have to change the ViewModel's code, the only change is required to properly set coroutine scope (and dispatcher) when putting ViewModel under test.
Add this to your unit test:
#get:Rule
open val coroutineTestRule = CoroutineTestRule()
#Before
fun injectTestCoroutineScope() {
// Inject TestCoroutineScope (coroutineTestRule itself is a TestCoroutineScope)
// to be used as ViewModel.viewModelScope fro the following reasons:
// 1. Let test fail if coroutine launched in ViewModel.viewModelScope throws exception;
// 2. Be able to advance time in tests with DelayController.
viewModel.injectScope(coroutineTestRule)
}
CoroutineTestRule.kt
#Suppress("EXPERIMENTAL_API_USAGE")
class CoroutineTestRule : TestRule, TestCoroutineScope by TestCoroutineScope() {
val dispatcher = coroutineContext[ContinuationInterceptor] as TestCoroutineDispatcher
override fun apply(
base: Statement,
description: Description?
) = object : Statement() {
override fun evaluate() {
Dispatchers.setMain(dispatcher)
base.evaluate()
cleanupTestCoroutines()
Dispatchers.resetMain()
}
}
}
The code will be executed sequentially (your test code, then view model code, then launched coroutine) due to the replaced main dispatcher.
The advantages of the approach above:
Write test code as normal, no need to use runBlocking or so;
Whenever a crash happen in coroutine, that will fail the test (because of cleanupTestCoroutines() called after every test).
You can test coroutine which uses delay internally. For that test code should be run in coroutineTestRule.runBlockingTest { } and advanceTimeBy() be used to move to the future.