`Caused by: java.lang.NullPointerException at rx....
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Caused by: java.lang.NullPointerException
	at rx.android.schedulers.LooperScheduler$HandlerWorker.schedule(LooperScheduler.java:77)
So maybe the Handler inside of HandlerWorker is null? Have you tried overriding the AndroidSchedulers.mainThread() with a TestScheduler?