A modern programming language that makes developers happier.

kotlinlang

Does `delay` use <https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.time/-time-source/-monotonic/|TimeSource.Monotonic>?

No. The dispatcher chooses how delay works.

If the dispatcher doesn't specify how delays work, by default, `System.nanoTime()` is used on the JVM: <https://github.com/Kotlin/kotlinx.coroutines/blob/b11abdf01d4d5db85247ab365abc72efc7b95062/kotlinx-coroutines-core/jvm/src/DefaultExecutor.kt#L101-L120|https://github.com/Kotlin/kotlinx.coroutines/blob/b11abdf01d4d5db85247ab365abc72efc7b95062/kotlinx-coroutines-core/jvm/src/DefaultExecutor.kt#L[…]20>

The TestDispatcher used by `runTest` skips delays by „just“ increasing the virtual time. 

If this question is testing related then you may want to _*<https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-test/kotlinx.coroutines.test/test-time-source.html|get>*_ a `TimeSource`  from the test dispatcher instead (and then pass that to your business logic):

And, you can convert the/a TimeSource to a kotlin.time.Clock too. 