Hello! I am a bit confused with the case, how can I cancel the flow job, since in tests sometimes ha...

# coroutines

[Zhanna Gorelova]

Hello! I am a bit confused with the case, how can I cancel the flow job, since in tests sometimes happens that after a 30 seconds the flow is still alive and does println(), but now other test is in processing. Since I pass context without job, there is no job and ensureActive returns true and I can’t cancel the job with flow. And context.cancel() as well cancels job, but there is no such in context. I thought that launch with flow should inherit parents Job, but what if there is no such? Thanks!

class CoroutineTest {
    @Test
    fun `test`() = withContext { context ->
        // when
        SomethingWithFlow(context)

        //then
        assertNotNull(context[Job])
    }

    private fun withContext(context: CoroutineContext = <http://Dispatchers.IO|Dispatchers.IO>, block: suspend (CoroutineContext) -> Unit) {
        runBlocking(context) { block(context) }
    }

    class SomethingWithFlow(override val coroutineContext: CoroutineContext) : CoroutineScope {
        private val flow = MutableStateFlow<String>("Initial")

        init {
            launch {
                flow.debounce(30_000L).collectLatest {
                    ensureActive()
                    println(it)
                }
            }
        }
    }
}

[Nick Allen]

If there's no Job in CoroutineScope, then you have to manage the coroutines individually. This is a rare but expected scenario. GlobalScope does not have a Job and can not be cancelled. To cancel collectLatest, you have to capture the Job returned by launch and cancel that.

The CoroutineScope interface docs recommend that the factory functions like CoroutineScope() are used to create an instance. You can use GlobalScope where you don't need a cancellable scope (like a process long coroutine in a singleton) and you can use CoroutineScope() or MainScope() when you do want to cancel the scope because these functions include a Job if it's not already there.

If you have a scope with the right Job (or lack of Job), then you can use + to create a new scope with the other `ContextElement`s that you want. If I wanted a non-cancellable scope for IO, I'd create it with GlobalScope + <http://Dispatchers.IO|Dispatchers.IO>.