Develop Reference

Problems with Kotlin Result<T> on unit tests

I am working on an android Application and I opted to use Kotlin Result class so as to handle success/failure on my operations. I made the changes to the code, but the tests stop working and I cannot understand why. Here I show you some snippets:
FireStoreClient.kt
suspend fun items(): Result<ItemsResponse>
NetworkDataSource.kt
suspend fun getItems(): List<Item> =
fireStoreClient.items().fold({ it.items.map { item -> item.toDomain() } }, { emptyList() })
NetworkDataSourceTest.kt
#ExperimentalCoroutinesApi
#Test
fun `Check getItems works properly`() = runBlockingTest {
whenever(fireStoreClient.items()).doReturn(success(MOCK_ITEMS_DOCUMENT))
val expectedResult = listOf(
Item(
id = 1,
desc = "Description 1"
),
Item(
id = 2,
desc = "Description 2"
)
)
assertEquals(expectedResult, dataSource.getItems())
}
And this is the exception I am getting right now. Any clue? It appears that the fold() method is not being executed when unit testing.
java.lang.ClassCastException: kotlin.Result cannot be cast to ItemsResponse
at NetworkDataSource.getItems(NetworkDataSource.kt:31)

I've found a different workaround for this result-wrapping issue, for those who don't want to make their own Result type.
This issue appears to happens specifically when using Mockito's .thenReturn on suspend functions. I've found that using .thenAnswer doesn't exhibit the problem.
So instead of writing this in your unit test (changed doReturn to thenReturn here):
whenever(fireStoreClient.items()).thenReturn(success(MOCK_ITEMS_DOCUMENT))
Use:
whenever(fireStoreClient.items()).thenAnswer { success(MOCK_ITEMS_DOCUMENT) }
Edit: I should note that I was still experiencing this issue when running Kotlin 1.5.0.
Edit: On Kotlin 1.5.20 I can use .thenReturn again.

After a deep dive into the problem, finally, I've found a temporary workaround that works in the testing environment. The problem is, somehow the value of the Result object is wrapped by another Result, and we can pull the desired value or exception using reflection.
So, I've created an extension function called mockSafeFold, which implements the fold behavior in normal calls, and acts fine when you are executing unit-tests.
inline fun <R, reified T> Result<T>.mockSafeFold(
onSuccess: (value: T) -> R,
onFailure: (exception: Throwable) -> R
): R = when {
isSuccess -> {
val value = getOrNull()
try {
onSuccess(value as T)
} catch (e: ClassCastException) {
// This block of code is only executed in testing environment, when we are mocking a
// function that returns a `Result` object.
val valueNotNull = value!!
if ((value as Result<*>).isSuccess) {
valueNotNull::class.java.getDeclaredField("value").let {
it.isAccessible = true
it.get(value) as T
}.let(onSuccess)
} else {
valueNotNull::class.java.getDeclaredField("value").let {
it.isAccessible = true
it.get(value)
}.let { failure ->
failure!!::class.java.getDeclaredField("exception").let {
it.isAccessible = true
it.get(failure) as Exception
}
}.let(onFailure)
}
}
}
else -> onFailure(exceptionOrNull() ?: Exception())
}
Then, simply call it instead of fold:
val result: Result = myUseCase(param)
result.mockSafeFold(
onSuccess = { /* do whatever */ },
onFailure = { /* do whatever */ }
)

I had the same issue.
I noticed that my method of injected class which should return Result<List<Any>> returns actually Result<Result<List<Any>>> which causes the ClassCastException. I used the Evaluate Expression option for the result from the method and I got
Success(Success([]))
The app works well but unit tests didn't pass due this problem.
As a temporary solution I built a new simple implementation of Result sealed class with fold() extension function. It should be easy to replace in future to kotlin.Result
Result sealed class:
sealed class Result<T> {
data class Success<T>(val value: T) : Result<T>()
data class Failure<T>(val error: Throwable) : Result<T>()
}
fold() extension function:
inline fun <R, T> Result<T>.fold(
onSuccess: (value: T) -> R,
onFailure: (exception: Throwable) -> R
): R = when (this) {
is Result.Success -> onSuccess(value)
is Result.Failure -> onFailure(error)
}

Unit testing coroutines runBlockingTest: This job has not completed yet

Please find below a function using a coroutine to replace callback :
override suspend fun signUp(authentication: Authentication): AuthenticationError {
return suspendCancellableCoroutine {
auth.createUserWithEmailAndPassword(authentication.email, authentication.password)
.addOnCompleteListener(activityLifeCycleService.getActivity()) { task ->
if (task.isSuccessful) {
it.resume(AuthenticationError.SignUpSuccess)
} else {
Log.w(this.javaClass.name, "createUserWithEmail:failure", task.exception)
it.resume(AuthenticationError.SignUpFail)
}
}
}
}
Now I would like to unit testing this function. I am using Mockk :
#Test
fun `signup() must be delegated to createUserWithEmailAndPassword()`() = runBlockingTest {
val listener = slot<OnCompleteListener<AuthResult>>()
val authentication = mockk<Authentication> {
every { email } returns "email"
every { password } returns "pswd"
}
val task = mockk<Task<AuthResult>> {
every { isSuccessful } returns true
}
every { auth.createUserWithEmailAndPassword("email", "pswd") } returns
mockk {
every { addOnCompleteListener(activity, capture(listener)) } returns mockk()
}
service.signUp(authentication)
listener.captured.onComplete(task)
}
Unfortunately this test failed due to the following exception : java.lang.IllegalStateException: This job has not completed yet
I tried to replace runBlockingTest with runBlocking but the test seems to wait in an infinite loop.
Can someone help me with this UT please?
Thanks in advance

As can be seen in this post:
This exception usually means that some coroutines from your tests were scheduled outside the test scope (more specifically the test dispatcher).
Instead of performing this:
private val networkContext: CoroutineContext = TestCoroutineDispatcher()
private val sut = Foo(
networkContext,
someInteractor
)
fun `some test`() = runBlockingTest() {
// given
...
// when
sut.foo()
// then
...
}
Create a test scope passing test dispatcher:
private val testDispatcher = TestCoroutineDispatcher()
private val testScope = TestCoroutineScope(testDispatcher)
private val networkContext: CoroutineContext = testDispatcher
private val sut = Foo(
networkContext,
someInteractor
)
Then in test perform testScope.runBlockingTest
fun `some test`() = testScope.runBlockingTest {
...
}
See also Craig Russell's "Unit Testing Coroutine Suspend Functions using TestCoroutineDispatcher"

In case of Flow testing:
Don't use flow.collect directly inside runBlockingTest. It should be wrapped in launch
Don't forget to cancel TestCoroutineScope in the end of a test. It will stop a Flow collecting.
Example:
class CoroutinesPlayground {
private val job = Job()
private val testDispatcher = StandardTestDispatcher()
private val testScope = TestScope(job + testDispatcher)
#Test
fun `play with coroutines here`() = testScope.runBlockingTest {
val flow = MutableSharedFlow<Int>()
launch {
flow.collect { value ->
println("Value: $value")
}
}
launch {
repeat(10) { value ->
flow.emit(value)
delay(1000)
}
job.cancel()
}
}
}

This is not an official solution, so use it at your own risk.
This is similar to what #azizbekian posted, but instead of calling runBlocking, you call launch.
As this is using TestCoroutineDispatcher, any tasks scheduled to be run without delay are immediately executed. This might not be suitable if you have several tasks running asynchronously.
It might not be suitable for every case but I hope that it helps for simple cases.
You can also follow up on this issue here:
https://github.com/Kotlin/kotlinx.coroutines/issues/1204
If you know how to solve this using the already existing runBlockingTest and runBlocking, please be so kind and share with the community.
class MyTest {
private val dispatcher = TestCoroutineDispatcher()
private val testScope = TestCoroutineScope(dispatcher)
#Test
fun myTest {
val apiService = mockk<ApiService>()
val repository = MyRepository(apiService)
testScope.launch {
repository.someSuspendedFunction()
}
verify { apiService.expectedFunctionToBeCalled() }
}
}

According to my understanding, this exception occurs when you are using a different dispatcher in your code inside the runBlockingTest { } block with the one that started runBlockingTest { }.
So in order to avoid this, you first have to make sure you inject Dispatchers in your code, instead of hardcoding it throughout your app. If you haven't done it, there's nowhere to begin because you cannot assign a test dispatcher to your test codes.
Then, in your BaseUnitTest, you should have something like this:
#get:Rule
val coroutineRule = CoroutineTestRule()
#ExperimentalCoroutinesApi
class CoroutineTestRule(
val testDispatcher: TestCoroutineDispatcher = TestCoroutineDispatcher()
) : TestWatcher() {
override fun finished(description: Description?) {
super.finished(description)
Dispatchers.setMain(testDispatcher)
}
override fun starting(description: Description?) {
super.starting(description)
Dispatchers.resetMain()
testDispatcher.cleanupTestCoroutines()
}
}
Next step really depends on how you do Depedency Injection. The main point is to make sure your test codes are using coroutineRule.testDispatcher after the injection.
Finally, call runBlockingTest { } from this testDispatcher:
#Test
fun `This should pass`() = coroutineRule.testDispatcher.runBlockingTest {
//Your test code where dispatcher is injected
}

There is an open issue for this problem: https://github.com/Kotlin/kotlinx.coroutines/issues/1204
The solution is to use the CoroutineScope intead of the TestCoroutinScope until the issue is resolved, you can do by replacing
#Test
fun `signup() must be delegated to createUserWithEmailAndPassword()`() =
runBlockingTest {
with
#Test
fun `signup() must be delegated to createUserWithEmailAndPassword()`() =
runBlocking {

None of these answers quite worked for my setup due to frequent changes in the coroutines API.
This specifically works using version 1.6.0 of kotlin-coroutines-test, added as a testImplementation dependency.
#Test
fun `test my function causes flow emission`() = runTest {
// calling this function will result in my flow emitting a value
viewModel.myPublicFunction("1234")
val job = launch {
// Force my flow to update via collect invocation
viewModel.myMemberFlow.collect()
}
// immediately cancel job
job.cancel()
assertEquals("1234", viewModel.myMemberFlow.value)
}

If you have any
Channel
inside the launch, you must call to
Channel.close()
Example code:
val channel = Channel<Success<Any>>()
val flow = channel.consumeAsFlow()
launch {
channel.send(Success(Any()))
channel.close()
}

runBlockingTest deprecated since 1.6.0 and replaced with runTest.

You need to swap arch background executor with one that execute tasks synchronously. eg. For room suspend functions, live data etc.
You need the following dependency for core testing
androidTestImplementation 'androidx.arch.core:core-testing:2.1.0'
Then add the following at the top of test class
#get:Rule
val instantExecutor = InstantTaskExecutorRule()
Explanations
InstantTaskExecutorRule A JUnit Test Rule that swaps the background executor used by the
Architecture Components with a different one which executes each task
synchronously.
You can use this rule for your host side tests that use Architecture
Components

As I mentioned here about fixing runBlockingTest, maybe it could help you too.
Add this dependency if you don't have it
testImplementation "androidx.arch.core:core-testing:$versions.testCoreTesting" (2.1.0)
Then in your test class declare InstantTaskExecutorRule rule:
#get:Rule
val instantTaskExecutorRule = InstantTaskExecutorRule()

JUnit 5 Annotations - Not Working with LiveData / Parameterized Tests

Overview
Expected Behavior
Replace mock object initialization using the mockObject function implementation with annotation syntax initialization for JUnit 5 as outlined in the documentation and Medium post by #oleksiyp.
Current Behavior
The test in question is a parameterized test as outlined by #phauer for JUnit 5 which seems to conflict with #ExtendWith(MockKExtension::class). In order to implement tests with LiveData the test must run synchronously in the local unit test using this InstantExecutorExtension designed by #JeroenMols.
Mock object initialization works as expected with the mockObject function, but fails using the annotation #MockK.
Error
Warning message/Build fail:
Repeatable annotations with non-SOURCE retention are not yet supported.
Implementation
mockObject function implementation (Working as expected)
#ExtendWith(InstantExecutorExtension::class)
class NavigateContentTests {
private val mainThreadSurrogate = newSingleThreadContext("UI thread")
private val contentViewModel = ContentViewModel()
// This is the stream of tests to run in the Parameterized test below.
private fun NavigateContent() = Stream.of(
NavigateContentTest(
isRealtime = false,
feedType = MAIN,
timeframe = DAY,
mockFeedList = mockDbContentListForDay,
mockContent = mockArticleContent),
...)
#BeforeAll
fun beforeAll() { mockkObject(ContentRepository) }
#AfterAll
fun afterAll() { unmockkAll() // Re-assigns transformation of object to original state prior to mock. }
#BeforeEach
fun beforeEach() { Dispatchers.setMain(mainThreadSurrogate) }
#AfterEach
fun afterEach() {
Dispatchers.resetMain() // Reset main dispatcher to the original Main dispatcher.
mainThreadSurrogate.close()
}
#ParameterizedTest
#MethodSource("NavigateContent")
fun `Navigate Content`(test: NavigateContentTest) = runBlocking {
every { ContentRepository.getMainFeedList(test.isRealtime, any()) } returns mockGetMainFeedList(
test.mockFeedList, CONTENT)
every {
ContentRepository.queryLabeledContentList(test.feedType)
} returns mockQueryMainContentList(test.mockFeedList)
every { ContentRepository.getContent(test.mockContent.id) } returns mockGetContent(test)
// Tests here...
// Verification here...
}
}
Annotation syntax initialization (Not working due to two extensions #ExtendWith)
#ExtendWith(InstantExecutorExtension::class)
#ExtendWith(MockKExtension::class)
class NavigateContentTests {
// This object should be mocked.
#MockK
lateinit var contentRepository: ContentRepository
private val mainThreadSurrogate = newSingleThreadContext("UI thread")
private val contentViewModel = ContentViewModel()
// This is the stream of tests to run in the Parameterized test below.
private fun NavigateContent() = Stream.of(
NavigateContentTest(
isRealtime = false,
feedType = MAIN,
timeframe = DAY,
mockFeedList = mockDbContentListForDay,
mockContent = mockArticleContent),
...)
#BeforeAll
fun beforeAll() { MockKAnnotations.init(this, relaxUnitFun = true) // turn relaxUnitFun on for }
#AfterAll
fun afterAll() { unmockkAll() // Re-assigns transformation of object to original state prior to mock. }
#BeforeEach
fun beforeEach() { Dispatchers.setMain(mainThreadSurrogate) }
#AfterEach
fun afterEach() {
Dispatchers.resetMain() // Reset main dispatcher to the original Main dispatcher.
mainThreadSurrogate.close()
}
#ParameterizedTest
#MethodSource("NavigateContent")
fun `Navigate Content`(test: NavigateContentTest) = runBlocking {
every { contentRepository.getMainFeedList(test.isRealtime, any()) } returns mockGetMainFeedList(
test.mockFeedList, CONTENT)
every {
contentRepository.queryLabeledContentList(test.feedType)
} returns mockQueryMainContentList(test.mockFeedList)
every { contentRepository.getContent(test.mockContent.id) } returns mockGetContent(test)
// Tests here...
// Verification here...
}
}
Environment
MockK version: 1.9.3
OS: Mac 10.14.6
Kotlin version: 1.3.50
JDK version: 12.0.1
JUnit version: 5.5.1
Type of test: Unit test

This is a bug according to this GitHub issue, as documented by the MockK creator, #oleksiy.
I will update this post once I see the bug is resolved.

Android: ViewModel test using kotlin coroutines not working

I'm using coroutines for the first time and I'm having troubles testing my work on a ViewModel.
The test fails with
Wanted but not invoked:
observer.onChanged(<Capturing argument>);
The test is the following:
val androidVersioningMock: Versioning.AndroidVersioning = mock {
on { required } doAnswer { "3.3.6" }
}
val versioningMock: Versioning = mock {
on { android } doAnswer { androidVersioningMock }
}
whenever(networkManager.getAppVersionAsync()).thenReturn(GlobalScope.async { versioningMock })
runBlocking {
updateVersionModel =
UpdateViewModel(application, coroutineDispatcherProvider).apply {
updateLiveData.observeForever(stateObserver)
}
verify(stateObserver).onChanged(stateCaptor.capture())
assertTrue(stateCaptor.lastValue is UpdateState.NoUpdate)
assertEquals(UpdateState.NoUpdate, stateCaptor.lastValue)
}
I have mocked the coroutineDispatcherProvider with
#ExperimentalCoroutinesApi
override val coroutineDispatcherProvider = mock<CoroutineDispatcherProvider> {
on { main } doAnswer { TestCoroutineContext() }
on { io } doAnswer { TestCoroutineContext() }
}
And in my ViewModel, the method that fails is
private suspend fun getUpdateVersion(): Versioning =
withContext(coroutineDispatcherProvider.io) {
networkManager.getAppVersionAsync().await()
}
which is executed like :
launch {
val versioningModel = getUpdateVersion()
...
}
Am I not mocking something or not doing something? Thanks in advance!

The TestCoroutineContext dispatcher is useful to handle timing within tests, but you want to run asynchronous calls synchronously. You should be able to achieve this with the Unconfined dispatcher.

I believe better approach is to pass dispatcher to viewModels, so tests are super easy..
see this https://stackoverflow.com/a/62629410/2719243

Kotlin coroutines using produces and mockito to mock the producing job

I am testing Kotlin coroutines in my Android app and I am trying to do the following unit test
#Test fun `When getVenues success calls explore venues net controller and forwards result to listener`() =
runBlocking {
val near = "Barcelona"
val result = buildMockVenues()
val producerJob = produce<List<VenueModel>>(coroutineContext) { result.value }
whenever(venuesRepository.getVenues(eq(near))) doReturn producerJob // produce corooutine called inside interactor.getVenues(..)
interactor.getVenues(near, success, error) // call to real method
verify(venuesRepository).getVenues(eq(near))
verify(success).invoke(argThat {
value == result.value
})
}
The interactor method is as follows
fun getVenues(near: String, success: Callback<GetVenuesResult>,
error: Callback<GetVenuesResult>) =
postExecute {
repository.getVenues(near).consumeEach { venues ->
if (venues.isEmpty()) {
error(GetVenuesResult(venues, Throwable("No venues where found")))
} else {
success(GetVenuesResult(venues))
}
}
}
postExecute{..} is a method on a BaseInteractor that executes the function in the ui thread through a custom Executor that uses the launch(UI) coroutine from kotlin android coroutines library
fun <T> postExecute(uiFun: suspend () -> T) =
executor.ui(uiFun)
Then the repository.getVenues(..) function is also a coroutine that returns the ProducerJob using produce(CommonPool) {}
The problem is that it seams that success callback in the interactor function doesn't seem to be executed as per the
verify(success).invoke(argThat {
value == result.value
})
However, I do see while debugging that the execution in the interactor function reaches to the if (venues.isEmpty()) line inside the consumeEach but then from there exits and continues with the test, obviously failing on the verify for the success callback.
I am a bit new on coroutines so any help would be appreciated.

I figured this one out. I saw that the problem was just with this producing coroutine and not with the others tests that are also using coroutines and working just fine. I noticed that I actually missed the send on the mocked ProducingJob in order to have it actually produce a value, in this case the list of mocks. I just added that changing the mock of the producing job to
val producerJob = produce { send(result.value) }