How to unit test that a MutableSharedFlow<T>(replay=0) has emitted a value?

Question

I'm not able to figure out how to test that a SharedFlow with replay=0 emitted a value.

import kotlinx.coroutines.flow.MutableSharedFlow
import kotlinx.coroutines.runBlocking
import org.junit.Test

class ShowcaseTest {

    @Test
    fun testIntSharedFlowFlow() {
        val intSharedFlow = MutableSharedFlow<Int>()

        runBlocking {
            intSharedFlow.emit(1)
        }
        
        // Does not work as there is no buffer because MutableSharedFlow(replay=0)
        assert(intSharedFlow.replayCache.first() == 1)
    }
}

Answer 1

You could use tryEmit() instead and verify the returned result

UPDATE:

Consider using Turbine For ex:

sharedFlow.test {
    sharedFlow.emit(1)
    assertEquals(expected = 1, expectItem())
    cancelAndIgnoreRemainingEvents()

}