Is there any way to be sure that a value in a flow has been collected by all collectors? :thread:

# coroutines

[vide]

Is there any way to be sure that a value in a flow has been collected by all collectors? 🧵

[vide]

val flow = MutableStateFlow(0)
val testScope = TestScope()
val defaultScope = CoroutineScope(Dispatchers.Default)
val values = mutableListOf<Int>()
testScope.launch { flow.collect { values.add(it) } }
repeat(1000) { n ->
    defaultScope.launch { flow.value = n }
    runBlocking { flow.first { it == n } }
    testScope.testScheduler.runCurrent()
    assertEquals(values[n], n)
}

[vide]

I would like to make sure that the collector running in testScope has collected before the assertion. I could wrap it in a loop that calls runCurrent() until it's done but I'm wondering if there's any other way.

[vide]

The stuff happening in defaultScope is not really part of the test, it is some external code listening for updates on a websocket connection. The test actually works like:

// mock update to websocket
flow.first { it == n }
testedScheduler.runCurrent()
// assert ui has updated