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Testing Kotlin flows by using toList() extension skips some emissions

I was testing some Kotlin Flows according to what the document mentioned in this part.
I created a FakeRepository and a FakeViewModel like this:
class FakeRepository {
private val flow = MutableSharedFlow<Int>()
suspend fun emit(value: Int) = flow.emit(value)
val scores: Flow<Int> = flow
}
class FakeViewModel(private val repository: FakeRepository) : ViewModel() {
val score: StateFlow<Int> = repository.scores
.stateIn(viewModelScope, SharingStarted.WhileSubscribed(), 0)
fun initialize() {
viewModelScope.launch {
//delay(100)
repository.emit(1)
//delay(100)
repository.emit(2)
//delay(100)
repository.emit(3)
//delay(100)
}
}
}
I also created a test class to test this score flow like this:
#ExperimentalCoroutinesApi
class FakeViewModelTest {
/*
Replace real dispatchers with instances of TestDispatchers to ensure that all
code runs on the single test thread.
*/
#get:Rule
val mainDispatcherRule = MainDispatcherRule()
#Test
fun testFakeRepository() = runTest {
val fakeRepository = FakeRepository()
val viewModel = FakeViewModel(fakeRepository)
val items = mutableListOf<Int>()
val job = launch(StandardTestDispatcher()) {
viewModel.score.toList(items)
}
viewModel.initialize()
advanceUntilIdle()
MatcherAssert.assertThat(items.size, Matchers.equalTo(4))
job.cancel()
}
}
When I run the test, surprisingly, it fails and says that the list size is 1.
But after uncommenting the delays, the test will be passed.
Why the test behave like this? As the document mentioned here, TestDispatcher will skip delays.
Did I misunderstand something? How can I fix it?

As the StateFlow documentation says:
Updates to the value are always conflated. So a slow collector skips fast updates, but always collects the most recently emitted value.
A StateFlow has no memory whatsoever of previous values. In your current code, the collector and the initialize function's coroutine are racing each other. There's no guarantee that the emitter will wait for an item to be collected before emitting the next.
The possible reason the delay calls make it work is that even with the TestDispatcher, it might be suspending (yielding the thread), which would give the other coroutine a chance to collect each item. Not sure, because I don't know the details of what these TestDispatchers do under the hood.
If you want to guarantee values aren't dropped, you need to use a SharedFlow with BufferOverflow.SUSPEND. Or you could give it a replay of Int.MAX_VALUE, but this could be unsustainable depending on your use case.

#BeforeAll not functioning as intended in JUnit5

I'm running UI testing on Android devices using Appium. We recently migrated to JUnit5 and I'm attempting to utilize the #BeforeAll class to make sure the app is in a good state before we continue to the next class.
Currently, the tooltip in Android studio is indicating that the function is never used. In the log I'm seeing a junitException saying that the method must be static. I haven't implemented #TestInstance yet, I'd like to be able to use beforeAll without it for now. I'm just confused why it isn't working since my #beforeEach and #afterEach are both working. The error and code are below.
org.junit.platform.commons.JUnitException: #BeforeAll method 'public final void com.bypass.automation.BaseTest.healthcheck()' must be static unless the test class is annotated with #TestInstance(Lifecycle.PER_CLASS).
open class BaseTest {
lateinit var driver: AndroidDriver<MobileElement>
private val capabilities = DesiredCapabilities().apply {
setCapability(APPIUM_VERSION, "1.19.1")
setCapability(PLATFORM_NAME, "Android")
setCapability(DEVICE_NAME, "Android")
setCapability("appPackage", "com.ourpackage")
setCapability("appActivity", "com.ourpackage.PassthroughHomeActivity")
setCapability("automationName", "uiautomator2")
setCapability("skipDeviceInitialization", true)
setCapability("noReset", true)
setCapability("full-reset", false)
setCapability("enableMultiWindows", false)
setCapability("unlockType", "pin")
setCapability("unlockKey", "0000")
setCapability("newCommandTimeout", "120")
}
#BeforeAll
fun healthcheck() {
val currentActivity = driver.currentActivity()
println("Current activity is $currentActivity")
if (currentActivity.contains("StationSecurePayActivity")) {
println("Exiting Station Pay")
CreditCardEntryView(driver).clickBackButton()
}
when {
currentActivity.contains("kiosk") -> {
Thread.sleep(2000)
println("Exiting Kiosk")
KioskView(driver).exitKiosk()
println("Logging out")
LogInProviderUtil(driver).logOut()
}
currentActivity != ".LoginActivity" -> {
println("Logging out")
LogInProviderUtil(driver).logOut()
}
currentActivity.contains(".LoginActivity") -> {
println("Session was properly logged out. No action taken.")
}
}
}
#BeforeEach
fun setup() {
driver = AndroidDriver(URL("http://127.0.0.1:4750/wd/hub"), capabilities)
driver.manage()?.timeouts()?.implicitlyWait(30, SECONDS)
if (LogInProviderUtil(driver).isLoggedIn()){
LogInProviderUtil(driver).logOut()
}
}
#AfterEach
fun teardown() {
if (LogInProviderUtil(driver).isLoggedIn()){
LogInProviderUtil(driver).logOut()
driver.quit()
}
else {
driver.quit()
}
}
}

It will work. I believe that any method annotated with #BeforeAll must be static (unless the "per-class" test instance lifecycle is used). So it sounds to me like you should switch to that by adding this annotation to your test class: #TestInstance(Lifecycle.PER_CLASS)
Also, it is usual practice to make your setup and teardown methods public. Also, I recommend use of Selenium-Jupiter framework (https://github.com/bonigarcia/selenium-jupiter/blob/master/README.md#appium) . Good luck.

If you want to have an initialization block you may put it simply into
init{} method. And you don't have to annotate it.

Getting error MockKException: no answer found for: Observer(#8).onChanged Android

I'm writing a unit test. Below is my code. The architecture is MVVM using Dagger2. I'm calling the login function residing in the LoginViewModel, which is notifying the getLoginState function. The error I'm getting is:
Error:
io.mockk.MockKException: no answer found for: Observer(#8).onChanged(Success(data=))
at io.mockk.impl.stub.MockKStub.defaultAnswer(MockKStub.kt:90)
LoginViewModelClass:
fun logIn(phone: String, phoneCode: String) {
loginState.value = Outcome.success("")
}
fun getLoginState(): LiveData<Outcome<String>> = loginState
LoginViewModelTest class:
#RelaxedMockK
var SUT: LoginViewModel? = null
#Mock
var loginInteractor: LoginInteractor? = null
#Mock
var textValidator: TextValidator? = null
#Mock
var textProvider: TextProvider? = null
#Mock
var blinkUserPreferences: BlinkUserPreferences? = null
#get:Rule
var rule: TestRule = InstantTaskExecutorRule()
#RelaxedMockK
var mockObserver: Observer<Outcome<String>>? = null
#Before
fun setUp() {
MockKAnnotations.init(this, relaxUnitFun = true)
SUT = spyk(
LoginViewModel(
mockk<LoginInteractor>(),
mockk<TextValidator>(relaxed = true),
mockk<TextProvider>(),
mockk<BlinkUserPreferences>()))
mockObserver = mockk<Observer<Outcome<String>>>()
SUT!!.getLoginState().observeForever(mockObserver!!)
}
#Test
fun logIn() {
//Arrange
every {SUT!!.getLoginState().value} returns Outcome.success("")
//Act
SUT!!.logIn("89989676","89998")
//Assert
verify() { mockObserver!!.onChanged(Outcome.success("abc")) }
}
Question:
In verification, why onChanged method is not being called, or what does it mean that no answer found for Observer().onChanged, how can I notify my onChanged method so I can verify it?

After watching this: https://mockk.io/#answers. It says
specify that the matched call answers with a code block scoped with
answer scope
I just posted this:
every { mockObserver!!.onChanged(any()) } answers {}
in the following test function and it worked.
#Test
fun logIn() {
//Arrange
every { mockObserver!!.onChanged(any()) } answers {}
every {SUT!!.getLoginState().value} returns Outcome.success("abc")
//Act
SUT!!.logIn("89989676","89998")
//Assert
verify() { mockObserver!!.onChanged(Outcome.success("abc")) }
}
According to my understanding, if you mockk a function, and you want to use its particular function you must use the every expression to tell framework that it will answer, because framework needs to know that it needs to answer something.
And if you want that all behaviour functions should also be added with mock with their implementation then you must spyk your class so that it gets the behaviour as well and then you can easily use the function without using expression every.
Please note that every expression is used for many cases like to get a mocked result out of that function, or just need to tell the framework that this function should answers this.
Please correct me through comments if I'm wrong, Ill update it.

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()

Unit testing coroutines on UI thread

I'm using coroutines to do an asynchronous call on pull to refresh like so:
class DataFragment : Fragment(), SwipeRefreshLayout.OnRefreshListener {
// other functions here
override fun onRefresh() {
loadDataAsync()
}
private fun loadDataAsync() = async(UI) {
swipeRefreshLayout?.isRefreshing = true
progressLayout?.showContent()
val data = async(CommonPool) {
service?.getData() // suspending function
}.await()
when {
data == null -> showError()
data.isEmpty() -> progressLayout?.showEmpty(null, parentActivity?.getString(R.string.no_data), null)
else -> {
dataAdapter?.updateData(data)
dataAdapter?.notifyDataSetChanged()
progressLayout?.showContent()
}
}
swipeRefreshLayout?.isRefreshing = false
}
}
Everything here works fine when I actually put it on a device. My error, empty, and data states are all handled well and the performance is good. However, I'm also trying to unit test it with Spek. My Spek test looks like this:
#RunWith(JUnitPlatform::class)
class DataFragmentTest : Spek({
describe("The DataFragment") {
var uut: DataFragment? = null
beforeEachTest {
uut = DataFragment()
}
// test other functions
describe("when onRefresh") {
beforeEachTest {
uut?.swipeRefreshLayout = mock()
uut?.onRefresh()
}
it("sets swipeRefreshLayout.isRefreshing to true") {
verify(uut?.swipeRefreshLayout)?.isRefreshing = true // says no interaction with mock
}
}
}
}
The test is failing because it says that there was no interaction with the uut?.swipeRefreshLayout mock. After some experimenting, it seems this is because I'm using the UI context via async(UI). If I make it just be a regular async, I can get the test to pass but then the app crashes because I'm modifying views outside of the UI thread.
Any ideas why this might be occurring? Also, if anyone has any better suggestions for doing this which will make it more testable, I'm all ears.
Thanks.
EDIT: Forgot to mention that I also tried wrapping the verify and the uut?.onRefresh() in a runBlocking, but I still had no success.

If you want to make things clean and consider using MVP architecture in the future you should understand that CourutineContext is external dependency, that should be injected via DI, or passed to your presenter. More details on topic.
The answer for your question is simple, you should use only Unconfined CourutineContext for your tests. (more)
To make things simple create an object e.g. Injection with:
package com.example
object Injection {
val uiContext : CourutineContext = UI
val bgContext : CourutineContext = CommonPool
}
and in test package create absolutely the same object but change to:
package com.example
object Injection {
val uiContext : CourutineContext = Unconfined
val bgContext : CourutineContext = Unconfined
}
and inside your class it will be something like:
val data = async(Injection.bgContext) {service?.getData()}.await()