Unit testing RxJava with a Completable.timer

Android Studio 3.5.2
RxJava2
Kotlin 1.3.50

I have the following class that acts like a timer.

class DelayTimerImp(private val scheduler: IScheduler)
    : DelayTimer {

    override fun createTimeout(delay: Long, timeUnites: TimeUnit): Completable {
        return Completable.timer(delay, TimeUnit.SECONDS, scheduler.main())
    }
}

And I am using it in a method like this:

private fun startTimeoutRequest(delay: Long) {
    compositeSubscription.add(delayTimer.createTimeout(delay, TimeUnit.SECONDS)
            .subscribeOn(schedulers.io())
            .subscribe(::timeoutHasExceeded, ::timeoutError))
}

And in my test class and it uses the TestScheduler to return the io thread. I am mocking the delayTimer. Even though I thenReturn(Completable.complete()) the methods in the timeOutHasExceeded never go into them. I am thinking that if Completable has completed in go into that method.

   @Test
    fun `should reload and show loading state`() {
        // Arrange
        whenever(delayTimer.createTimeout(10, TimeUnit.SECONDS))
                .thenReturn(Completable.complete())

        // Act
        vipInformationPresenterImp.tryAgainTapped()

        // Assert methods in the timeOutHasExceeded
    }

Also If I change the following to this by changing the delay to 1:

whenever(delayTimer.createTimeout(1, TimeUnit.SECONDS))
                .thenReturn(Completable.complete())

I will get a crash on the following line:

.subscribeOn(schedulers.io())

What is the best way to unit test this?

Many thanks in advance

from Unit testing RxJava with a Completable.timer