`Dispatchers.setMain(coroutineContext[CoroutineDispatcher])` executes coroutines continuously about kotest HOT 10 CLOSED

No you don't. My bad, didn't see you had it enabled already.

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The docs say that runTest skips delays, but not that it executes eagerly.

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A side note: as explained in this Slack conversation, actually why the test never finished was because I never canceled viewModelScope and the while (true) loop ran forever.

The solution is to inject backgroundScope into MyViewModel() for tests, to replace viewModelScope. Also then there's no need to call Dispatchers.setMain().

from kotest.

can you try enabling coroutineTestScope?

    "never finishes".config(coroutineTestScope = true) {
        // The dispatcher from coroutineContext executes the `while(true)` loop continuously and without waiting for the delay
        // The test never finishes
        Dispatchers.setMain(coroutineContext[CoroutineDispatcher]!!)

        MyViewModel()
        println("test 2 finished") // Never comes this far
    }

from kotest.

Isn't it enough that it's enabled for the whole spec, do I need to additionally enable it for every test as well?

from kotest.

My suspicion is, Kotest uses UnconfinedTestDispatcher under the hood, which executes coroutines eagerly.
Generally StandardTestDispatcher is recommended by the coroutines team for testing.

from kotest.

We use the runTest function to launch the test. According to docs there it will execute eagerly and skip delays, which seems a bit undesired if we also want to provide access to the testCoroutineScheduler (as documented here) to allow control of time etc...

Do you suggest we should launch the test body in a new coroutine using the StandardTestDispatcher instead of using runTest?

from kotest.

At least the migration guide suggests that runTest uses StandardTestDispatcher.

from kotest.

It does, but it also advances time until idle, which is never the case with your sample.. Try executing your test with runTest directly and you should see the same issue

from kotest.

You're right, I could reproduce the same behavior using runTest in JUnit. Turns out I didn't understand how runTest works.

import org.junit.jupiter.api.Test

class MyViewModelTest {

    val testScheduler = TestCoroutineScheduler()
    val testDispatcher = StandardTestDispatcher(testScheduler)

    @OptIn(ExperimentalCoroutinesApi::class)
    @Test
    fun `runs correctly`() = runTest {
        Dispatchers.setMain(testDispatcher)

        MyViewModel()
        println("test 1; MyViewModel created")
        [email protected](2000)
        println("test 1; after advanceTimeBy")
    }

    @OptIn(ExperimentalStdlibApi::class, ExperimentalCoroutinesApi::class)
    @Test
    fun `never finishes`() = runTest {
        Dispatchers.setMain(coroutineContext[CoroutineDispatcher]!!)

        MyViewModel()
        println("test 2 finished") // Never finishes
    }
}

Thank you for your explanations!

from kotest.