How do you test your program using the arm virtual hardware simulator?

I saw the example in your online tutorial.

It was not clear to me what it is exactly that you are testing?

I mean you build the solution and then run it. And the test passes. Based on what? I mean how do you know the program ran as you expected?

Is there any way to change variables and read them to validate your program run? Basically implementing some kind of unit testing framework with a mocking framework and run them on the simulator? Otherwise, I didn't get the point of all this - as in what are you testing? How do you define a run as a pass and how do you define it as a fail?

Thanks,

Eyal