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How to manage coroutines in MainActivity with waiting until done?

I use GlobalScope with runBlocking in MainActivity, but I do not use there a flow just suspend function. I would like to change GlobalScope to other Scope from Coroutines.
UseCase
class UpdateNotificationListItemUseCase #Inject constructor(private val notificationDao: NotificationDao): BaseUpdateBooleanUseCase<Int, Boolean, Boolean, Boolean, Unit>() {
override suspend fun create(itemId: Int, isRead: Boolean, isArchived: Boolean, isAccepted: Boolean){
notificationDao.updateBooleans(itemId, isRead, isArchived, isAccepted)
}
}
MainActivity
val job = GlobalScope.launch { vm.getIdWithUpdate() }
runBlocking {
job.join()
}
MainViewmodel
suspend fun getIdWithUpdate() {
var id = ""
id = notificationAppSessionStorage.getString(
notificationAppSessionStorage.getIncomingKeyValueStorage(),
""
)
if (id != "") {
updateNotificationListItemUseCase.build(id.toInt(), true, false, false)
}
}
}
My proposition:
I have read documentation https://developer.android.com/kotlin/coroutines/coroutines-best-practices
val IODispatcher: CoroutineDispatcher = Dispatchers.IO
val externalScope: CoroutineScope = CoroutineScope(IODispatcher)
suspend {
externalScope.launch(IODispatcher) {
vm.getIdWithUpdate()
}.join()
}
Second option, but here I do not wait until job is done
suspend {
withContext(Dispatchers.IO) {
vm.getIdWithUpdate()
}
}
What do you think about it?
Doesn't it provide to ANR, I also block thread.

You can use lifecycleScope in MainActivity, instead of GlobalScope, to launch a coroutine :
lifecycleScope.launch {
vm.getIdWithUpdate() // calling suspend function
// here suspend function `vm.getIdWithUpdate()` finished execution
// ... do something after suspend function is done
}
To use lifecycleScope add dependency:
implementation 'androidx.lifecycle:lifecycle-runtime-ktx:$2.4.0'
GlobalScope is highly discouraged to use. And there is no need to call job.join(), you can do something in the coroutine builder block after calling vm.getIdWithUpdate(), for example update UI. This coroutine is running using Dispatchers.Main context.

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.

Coroutines unit tests pass individually but not when run together

I have two coroutines tests that both pass when run individually, but if I run them together the second one always fails (even if I switch them around!). The error I get is:
Wanted but not invoked: observer.onChanged([SomeObject(someValue=test2)]);
Actually, there were zero interactions with this mock.
There's probably something fundamental I don't understand about coroutines (or testing in general) and doing something wrong.
If I debug the tests I find that the failing test is not waiting for the inner runBlocking to complete. Actually the reason I have the inner runBlocking in the first place is to solve this exact problem and it seemed to work for individual tests.
Any ideas as to why this might be happening?
Test class
#ExperimentalCoroutinesApi
#RunWith(MockitoJUnitRunner::class)
class ViewModelTest {
#get:Rule
val instantTaskExecutorRule = InstantTaskExecutorRule()
private lateinit var mainThreadSurrogate: ExecutorCoroutineDispatcher
#Mock
lateinit var repository: DataSource
#Mock
lateinit var observer: Observer<List<SomeObject>>
private lateinit var viewModel: SomeViewModel
#Before
fun setUp() {
mainThreadSurrogate = newSingleThreadContext("UI thread")
Dispatchers.setMain(mainThreadSurrogate)
viewModel = SomeViewModel(repository)
}
#After
fun tearDown() {
Dispatchers.resetMain()
mainThreadSurrogate.close()
}
#Test
fun `loadObjects1 should get objects1`() = runBlocking {
viewModel.someObjects1.observeForever(observer)
val expectedResult = listOf(SomeObject("test1"))
`when`(repository.getSomeObjects1Async())
.thenReturn(expectedResult)
runBlocking {
viewModel.loadSomeobjects1()
}
verify(observer).onChanged(listOf(SomeObject("test1")))
}
#Test
fun `loadObjects2 should get objects2`() = runBlocking {
viewModel.someObjects2.observeForever(observer)
val expectedResult = listOf(SomeObject("test2"))
`when`(repository.getSomeObjects2Async())
.thenReturn(expectedResult)
runBlocking {
viewModel.loadSomeObjects2()
}
verify(observer).onChanged(listOf(SomeObject("test2")))
}
}
ViewModel
class SomeViewModel constructor(private val repository: DataSource) :
ViewModel(), CoroutineScope {
override val coroutineContext: CoroutineContext
get() = Dispatchers.Main
private var objects1Job: Job? = null
private var objects2Job: Job? = null
val someObjects1 = MutableLiveData<List<SomeObject>>()
val someObjects2 = MutableLiveData<List<SomeObject>>()
fun loadSomeObjects1() {
objects1Job = launch {
val objects1Result = repository.getSomeObjects1Async()
objects1.value = objects1Result
}
}
fun loadSomeObjects2() {
objects2Job = launch {
val objects2Result = repository.getSomeObjects2Async()
objects2.value = objects2Result
}
}
override fun onCleared() {
super.onCleared()
objects1Job?.cancel()
objects2Job?.cancel()
}
}
Repository
class Repository(private val remoteDataSource: DataSource) : DataSource {
override suspend fun getSomeObjects1Async(): List<SomeObject> {
return remoteDataSource.getSomeObjects1Async()
}
override suspend fun getSomeObjects2Async(): List<SomeObject> {
return remoteDataSource.getSomeObjects2Async()
}
}

When you use launch, you're creating a coroutine which will execute asynchronously. Using runBlocking does nothing to affect that.
Your tests are failing because the stuff inside your launches will happen, but hasn't happened yet.
The simplest way to ensure that your launches have executed before doing any assertions is to call .join() on them.
fun someLaunch() : Job = launch {
foo()
}
#Test
fun `test some launch`() = runBlocking {
someLaunch().join()
verify { foo() }
}
Instead of saving off individual Jobs in your ViewModel, in onCleared() you can implement your CoroutineScope like so:
class MyViewModel : ViewModel(), CoroutineScope {
private val job = SupervisorJob()
override val coroutineContext : CoroutineContext
get() = job + Dispatchers.Main
override fun onCleared() {
super.onCleared()
job.cancel()
}
}
All launches which happen within a CoroutineScope become children of that CoroutineScope, so if you cancel that job (which is effectively cancelling the CoroutineScope), then you cancel all coroutines executing within that scope.
So, once you've cleaned up your CoroutineScope implementation, you can make your ViewModel functions just return Jobs:
fun loadSomeObjects1() = launch {
val objects1Result = repository.getSomeObjects1Async()
objects1.value = objects1Result
}
and now you can test them easily with a .join():
#Test
fun `loadObjects1 should get objects1`() = runBlocking {
viewModel.someObjects1.observeForever(observer)
val expectedResult = listOf(SomeObject("test1"))
`when`(repository.getSomeObjects1Async())
.thenReturn(expectedResult)
viewModel.loadSomeobjects1().join()
verify(observer).onChanged(listOf(SomeObject("test1")))
}
I also noticed that you're using Dispatchers.Main for your ViewModel. This means that you will by default execute all coroutines on the main thread. You should think about whether that's really something that you want to do. After all, very few non-UI things in Android need to be done on the main thread, and your ViewModel shouldn't be manipulating the UI directly.

Coroutines best way to use

I am new to coroutines. SO I just wanted to know what is the best way to use them.
My scenraio/use case is I want to make a API call on IO thread and observe the results on Main thread and update the UI. Also when fragment's onDestoryView() is called, then I want to cancel my job.
My fragment asks the presenter for some updates. So my presenter has a coroutine running like this -
class MyPresenter(view: MyView,
private val coroutineCtx: CoroutineContext = Dispatchers.Main) : CoroutineScope {
private val job: Job = Job()
private var view: MyView? = null
init {
this.view= view
}
override val coroutineContext: CoroutineContext
get() = job + coroutineCtx
fun updateData() = launch{
//repo is singleton
val scanResult = repo.updateData()
when(scanResult) {
sucess -> { this.view.showSuccess()}
}
}
fun stopUpdate() {
job.cancel()
}
}
In my repository,
suspend fun updateData(): Result<Void> {
val response = API.update().await()
return response
}
Am I using coroutines correctly? If yes, my job.cancel() never seems to work although I call it from fragment's onDestroyView().

From my point of view you are using coroutine correctly. A few notes:
You don't have to pass view: MyView to the constructor, and assign its value to the property in init block. Instead you can mark view parameter in the constructor as val and it will became a property:
class MyPresenter(private val view: MyView,
private val coroutineCtx: CoroutineContext = Dispatchers.Main) : CoroutineScope {
// you can get rid of the next lines:
private var view: MyView? = null
init {
this.view= view
}
}
launch function returns a Job. You can add an extension function, e.g. launchSilent, to return Unit :
fun CoroutineScope.launchSilent(
context: CoroutineContext = EmptyCoroutineContext,
start: CoroutineStart = CoroutineStart.DEFAULT,
block: suspend CoroutineScope.() -> Unit
) {
launch(context, start, block)
}
From my observation job.cancel() works correctly: when you invoke it a coroutine must stop. For example if we put some logs:
fun updateData() = launch{
Log.d("Tag", "launch start")
val scanResult = repo.updateData()
when(scanResult) {
success -> { this.view.showSuccess()}
}
Log.d("Tag", "launch end")
}
And add some delay to the repo's updateData() function:
suspend fun updateData(): Result<Void> {
delay(5000)
val response = API.update().await()
return response
}
And, for example, in the fragment after invoking presenter.updateData() we call something like Handler().postDelayed({ presenter.stopUpdate() }, 3000) we won't see "launch end" log in the Logcat.

How to unit test coroutine when it contains coroutine delay?

When I add a coroutine delay() in my view model, the remaining part of the code will not be executed.
This is my demo code:
class SimpleViewModel : ViewModel(), CoroutineScope {
override val coroutineContext: CoroutineContext
get() = Dispatchers.Unconfined
var data = 0
fun doSomething() {
launch {
delay(1000)
data = 1
}
}
}
class ScopedViewModelTest {
#Test
fun coroutineDelay() {
// Arrange
val viewModel = SimpleViewModel()
// ActTes
viewModel.doSomething()
// Assert
Assert.assertEquals(1, viewModel.data)
}
}
I got the assertion result:
java.lang.AssertionError:
Expected :1
Actual :0
Any idea how to fix this?

You start a coroutine which suspends for 1 second before setting data to 1. Your test just invokes doSomething but does not wait until data is actually being set. If you add another, longer delay, to the test it will, work:
#Test
fun coroutineDelay() = runBlocking {
...
viewModel.doSomething()
delay(1100)
...
}
You can also make the coroutine return a Deferred which you can wait on:
fun doSomething(): Deferred<Unit> {
return async {
delay(1000)
data = 1
}
}
With await there's no need to delay your code anymore:
val model = SimpleViewModel()
model.doSomething().await()

The first issue in your code is that SimpleViewModel.coroutineContext has no Job associated with it. The whole point of making your view model a CoroutineScope is the ability to centralize the cancelling of all coroutines it starts. So add the job as follows (note the absence of a custom getter):
class SimpleViewModel : ViewModel(), CoroutineScope {
override val coroutineContext = Job() + Dispatchers.Unconfined
var data = 0
fun doSomething() {
launch {
delay(1000)
data = 1
}
}
}
Now your test code can ensure it proceeds to the assertions only after all the jobs your view model launched are done:
class ScopedViewModelTest {
#Test
fun coroutineDelay() {
// Arrange
val viewModel = SimpleViewModel()
// ActTes
viewModel.doSomething()
// Assert
runBlocking {
viewModel.coroutineContext[Job]!!.children.forEach { it.join() }
}
Assert.assertEquals(1, viewModel.data)
}
}