Would you please help me with the following I want to test t kotlinlang #coroutines

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Title

Erik

12/03/2020, 5:47 PM

Would you please help me with the following? I want to test that the buffer size of my

MutableSharedFlow<T>(replay = 0, extraBufferCapacity = 1, onBufferOverflow = BufferOverflow.DROP_OLDEST)

equals

(in reality it's variable). I can't figure out how to get this working in a unit test: every time I emit something it is immediately collected (I use Turbine to

test

the flow). I basically want to emit 2 items and verify that only the last one is collected, the oldest is dropped.

👍 1

Maybe it's related to the unconfined dispatcher used by Turbine: I cannot pause that dispatcher, because it's not my test dispatcher?

This works:

@Test
    fun test() = testCoroutineDispatcher.runBlockingTest {
        val flow = MutableSharedFlow<Int>(
            replay = 0,
            extraBufferCapacity = 1,
            BufferOverflow.DROP_OLDEST
        )

        val emissions = mutableListOf<Int>()

        val subscription = flow.onEach { emissions += it }.launchIn(this)

        pauseDispatcher()
        flow.tryEmit(1)
        flow.tryEmit(2)
        resumeDispatcher()

        assertEquals(2, emissions.single())

        subscription.cancel()
    }

But it's not very pretty, because it's somewhat imperative

Using Turbine I'd like to do:

@Test
    fun test() = testCoroutineDispatcher.runBlockingTest {
        val flow = MutableSharedFlow<Int>(
            replay = 0,
            extraBufferCapacity = 1,
            BufferOverflow.DROP_OLDEST
        )

        flow.test {
            pauseDispatcher()
            flow.tryEmit(1)
            flow.tryEmit(2)
            resumeDispatcher()

            assertEquals(2, expectItem())
            expectNoEvents()
        }
    }

but that fails with:

java.lang.AssertionError: 
Expected :2
Actual   :1

Likely because of what I said: Turbine collects on the unconfined dispatcher, not my test coroutine dispatcher

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