You may already know that in RxJS Observables produce values over time. And the moment when exactly value will be emitted is controlled by a special entity - scheduler.
Knowing how schedulers work is extremely important in understanding how to unit test your async code.
Want to learn what are schedulers? Watch this video:
This video is a part of my free video-course "RxJS unit testing in Angular application. The whole picture.". You can get it by this link