What's the proper way to test if a flow collector received a value emitted by a sharedflow? using

runTest

doesn't seem to wait for a collector running in another scope to fully process the emitted value before returning. Keeping everything in the runTest scope and context just hangs the test because Flow.collect on a sharedflow never returns.

https://github.com/cashapp/turbine might help?

I found this article: https://jeff-padgett.medium.com/unit-testing-mutablesharedflow-12aec5b6e05 Which was a bit outdated because it used runBlockingTest. I tried it with:

@Test
    fun `does this even work`() {
        val emitter = MutableSharedFlow<String>()
        var emitted: String? = null
        runTest {
            val job = launch {
                emitter.collect { emitted = it }
            }
            emitter.emit("new value")

            job.cancel()
        }
        assertEquals("new value", emitted)
    }

But this test failed. Upon further investigation, replacing

runTest

with

runTest(UnconfinedTestDispatcher())

(to get similar behavior as

runBlockingTest

) is what made it pass. Fingers crossed this remains consistent.

That test will fail most likely due to the job being canceled before the block inside of launch is called

That's what was happening with

runTest

on its own, but the

UnconfinedTestDispatcher

"eagerly enters all launch calls," so it actually behaves as I'd like it to.

launch(start = CoroutineStart.UNDISPATCHED)

could also work more how you’re expecting

True, though, my actual use case is a bit more complicated than the simplified example. The

launch

call is happing in production code, so I'm getting it to pass by providing the production code with a coroutine scope that will behave the way I need 🙂