Think of an Observable/Flowable created with the Observable.interval() / Flowable.interval() factory method. If you have given a long interval (say five minutes) in them and have tested at least say 100 emissions then it would take a long time for testing to complete (500 minutes = 8.3 hours, that is, a complete man-hour just to test a single producer). Now if you have more producers like that with a larger interval and more emissions to test then it would probably take the whole lifetime to test, when would you ship the product then?
TestScheduler is here to save your life. They can effectively simulate time with time-driven producers so that we can do assertions by fast-forwarding it by a specific amount.
So, ...
