TestScheduler is a synchronous Scheduler that has to run on a single thread and its main purpose is to force async operators to execute synchronously as well.

Is there a reason you wanted this change?

Humm. This is the crash I was trying to fix, looked like a race but perhaps I'm using the testscheduler incorrectly somehow.

java.lang.NullPointerException
at rx.schedulers.TestScheduler$TimedAction.access$200(TestScheduler.java:37)
at rx.schedulers.TestScheduler.triggerActions(TestScheduler.java:111)
at rx.schedulers.TestScheduler.advanceTimeTo(TestScheduler.java:97)
at rx.schedulers.TestScheduler.advanceTimeBy(TestScheduler.java:84)

My class under test is subscribing to the scheduler asynchronously, I guess you're saying TestScheduler wasn't designed to operate list this?

Observable.interval(mPollTimeMinutes, TimeUnit.MINUTES, mScheduler)
.subscribeOn(Schedulers.newThread()).subscribe(v -> {
getMyUpgrade();
}, v -> {
});

It won't work with regular schedulers, for example:

Observable.interval(1, TimeUnit.MILLISECONDS) // <-- note: it uses the default computation() scheduler
.observeOn(testScheduler)
.subscribe();

is prone to concurrency issues.

If you use TestScheduler, it has to be applied everywhere.

Thanks for helping - is this how it's intended to be used?

Observable.interval(1, TimeUnit.MILLISECONDS, test ? testScheduler : Schedulers.computation())
.observeOn(test ? testScheduler : Schedulers.newThread())
.subscribe();

Yes.

Awesome, thanks.