What is the right way to testing a `MutableSharedF...

# flow

[Jeziel Lago]

What is the right way to testing a MutableSharedFlow ?

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

        intSharedFlow.emit(5)

        assertEquals(5, intSharedFlow.single())
    }

This code results java.lang.IllegalStateException: This job has not completed yet

[ephemient]

.single() can't work on a SharedFlow, since it never terminates

[ephemient]

val intSharedFlow = MutableSharedFlow<Int>(replay = 1)
intSharedFlow.emit(5)
assertEquals(5, intSharedFlow.first())

I'd expect that to work

[Javier]

Try turbine library

[Jeziel Lago]

@ephemient first() not works.

[ephemient]

@Jeziel Lago you're sure you added replay = 1 as well? the default replay = 0 doesn't work with this

[Jeziel Lago]

Using replay = 1 it works, but I need replay = 0.

[Javier]

maybe toList().first()?

[Jeziel Lago]

toList().first() not works too.
Turbine library seems a good option. Thanks @Javier
I’m disappointed with the Kotlin test library does not work with this use case.

[Javier]

Really I think we need a coroutines test framework

[ephemient]

you have a race condition with replay = 0 - need to subscribe to the flow before emitting

[ephemient]

with Turbine you could probably do something like

val intSharedFlow = MutableSharedFlow<Int>()
intSharedFlow.test {
    intSharedFlow.emit(5)
    assertEquals(5, expectItem())
}

[Jeziel Lago]

Turbine works well here. Thanks @ephemient

[Jeziel Lago]

@elizarov any plans for including something like Turbine (for MutableSharedFlow) in Kotlin Coroutine Test library?

[elizarov]

What's wrong with Turbine that you want an alternative?

[Jeziel Lago]

For me, Turbine is an excellent library, and I think nothing is wrong with it.
But we have a library to deal with test kotlinx-coroutines-test, which has a goal: provides testing utilities for effectively testing coroutines, that not help us so much (testing MutableSharedFlow as an example).
IMHO, is very important to provide utilities (or ways and to show how) to test new components when releasing them to the community.
Thanks all for helping me!