Can someone explain to me why it works with `Uncon...

# coroutines

[jean]

Can someone explain to me why it works with UnconfinedTestDispatcher and not with StandardTestDispatcher ?

private val testCoroutineDispatcher = UnconfinedTestDispatcher()
private val testCoroutineScope = TestScope(testCoroutineDispatcher)
private val testContext = ApplicationProvider.getApplicationContext<Context>()

private val sessionRepository: SessionRepository =
    PersistentSessionRepository(
        DataStoreFactory.create(
            serializer = SessionPreferencesSerializer,
            scope = testCoroutineScope,
            produceFile = { testContext.preferencesDataStoreFile("test-session-preferences") }
        ),
        routeRepository = routeRepository,
    )

@Test
fun sessionShouldInitiallyBeNull() = runTest(testCoroutineDispatcher, 5000) {
    assertNull(sessionRepository.session())
}

When I use StandardTestDispatcher I get this error :

After waiting for 60000 ms, the test coroutine is not completing

kotlinx.coroutines.test.UncompletedCoroutinesError: After waiting for 60000 ms, the test coroutine is not completing

[Dmitry Khalanskiy [JB]]

Not sure if it's related to your problem (probably it is), but it's incorrect to create a TestScope and not call runTest on it. runTest(testCoroutineDispatcher, 5000) → testCoroutineScope.runTest

[jean]

if I use testCoroutineScope.runTest then I get this :

Channel was closed

kotlinx.coroutines.channels.ClosedSendChannelException: Channel was closed

[Dmitry Khalanskiy [JB]]

Well, there you have it. The test fails with an exception for some reason, and now you see the reason. Before using testCoroutineScope in runTest that exception was just swallowed.

[jean]

override suspend fun session() = dataStore.data
    .firstOrNull()
    ?.let { wrapperToSession(it) }

What would cause a channel to close with this? I’m just trying to get the current value of a DataStore on which I don’t have control

[Dmitry Khalanskiy [JB]]

I don't have any idea about what DataStore is, maybe someone else can answer this. From what I see, the test code itself doesn't fail (or not using testCoroutineScope in runTest wouldn't matter). Rather, something else that uses this scope fails with the exception. I suggest looking more closely at the stacktrace to find the specific code that fails.

[Sam]

Perhaps passing scope = testCoroutineScope.backgroundScope to the DataStoreFactory would help?

[Dmitry Khalanskiy [JB]]

Unlikely. backgroundScope helps with the test hanging due to background work being executed, but this is the case of the producer failing for some reason, so the consumer times out when waiting.

[jean]

DataStore is a part of android jetpack.
But as you suggested I ran the test with stacktrace and turned out I forgot to also use testCoroutineScope.runTest on a @After test function that clears my store.
After updating it, I have another issue : Only a single call to runTest can be performed during one test

[Dmitry Khalanskiy [JB]]

Yep, what it says. Try using just runBlocking in @After. Or maybe it's possible not to use coroutines in @After at all.

[jean]

Yes so if I change my code to this it works, thanks for the help!

@Test
fun sessionShouldInitiallyBeNull() = testCoroutineScope.runTest {
    assertNull(journeySessionRepository.journeySession())
    journeySessionRepository.clearSession()
}