How does one get a manually created

CoroutineScope

to use a `TestScope`'s scheduler in

kotlinx-coroutines-test:1.6.1

for the virtual time behaviour? I would have expected

CoroutineScope(Job() + testScheduler)

to work but it doesn't. (Note that

CoroutineScope(Job() + coroutineContext)

does work but then when I try to cancel

differentScope

it fails the test because it cancels the parent

TestScope

, making it hard to test code that uses structured concurrency)

fun tickTest() = runTest {
        val differentScope = CoroutineScope(Job() + testScheduler)

        val ticks = mutableListOf<Int>()

        val tickJob = differentScope.launch {
            var time = 0
            while (true) {
                delay(1_000)
                ticks.add(++time)
            }
        }

        advanceTimeBy(5_001)

        tickJob.cancel()

        println(ticks)
        assert(ticks.size == 5)
    }

@Ridwan Farouki Try this

val differentScope = CoroutineScope(Job() + coroutineContext[ContinuationInterceptor]!!)

Thank you @julian, it does indeed work!

Also, the reason

CoroutineScope(Job() + coroutineContext)

cancels the

TestScope

job is that the rightmost context element wins when adding. Since

coroutineContext

is rightmost and contains a job, that job overwrites the one on the left of the

+

. This, though, would do what you want:

CoroutineScope(coroutineContext + Job())

, and then later,

differentScope.cancel()

.

I see, that makes sense, thanks for explaining. The important (and, IMO, rather esoteric) note that the

+

operator is not commutative caught me off guard.

Another option is

CoroutineScope(StandardTestDispatcher(testScheduler) + Job())

(here, the order doesn't matter), or even just

CoroutineScope(StandardTestDispatcher(testScheduler))

because

CoroutineScope

adds a

Job

if none is specifie. This creates a new dispatcher that is linked to the test framework.