I’m writing some documentation for my team around ...

# flow

[Peter Farlow]

I’m writing some documentation for my team around testing with Flows and I’ve found a simple example that I don’t understand.
Given a class that exposes both a suspending and non-suspending way to add a value to a SharedFlow:

class MyFlowRepository(private val applicationScope: CoroutineScope) {
    private val mutableSharedFlow = MutableSharedFlow<Data>()

    val dataFlow = mutableSharedFlow
        .shareIn(applicationScope, SharingStarted.Eagerly, replay = 1)

    suspend fun addDataSuspending(data: Data) {
        mutableSharedFlow.emit(data)
    }

    fun addData(data: Data) {
        applicationScope.launch {
            mutableSharedFlow.emit(data)
        }
    }
}

[Peter Farlow]

This test fails:

class MyFlowRepositoryTest {
    private val testScope = TestScope()

    @Test
    fun test() = testScope.runTest(dispatchTimeoutMs = 2_000) {
        val repository = MyFlowRepository(testScope.backgroundScope)
        repository.dataFlow.test {
            repository.addDataSuspending(Data("11"))
            assertEquals(expected = Data("11"), awaitItem())

            repository.addData(Data("10"))
            assertEquals(expected = Data("10"), awaitItem())
        }
    }
}

[Peter Farlow]

but if I reverse the order of the two calls in the test code, it passes:

@Test
    fun test() = testScope.runTest(dispatchTimeoutMs = 2_000) {
        val repository = MyFlowRepository(testScope.backgroundScope)
        repository.dataFlow.test {
            repository.addData(Data("10"))
            assertEquals(expected = Data("10"), awaitItem())

            repository.addDataSuspending(Data("11"))
            assertEquals(expected = Data("11"), awaitItem())
        }
    }

[Peter Farlow]

Why does the order affect the test outcome here?