I went through the documentation of

suspendCancellableCoroutine

. It mentions that this function throws a

CancellationException

if the coroutine is cancelled or completed while suspended. In which case the coroutine is completed while suspended?

This case is not trivial to set up. It never happens if you use coroutine builders from

kotlinx.coroutines

. Take a look at this test that tests for this schenario: https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-core/common/test/CancellableContinuationTest.kt#L120-L141

Thanks @elizarov. This unit test example really helped