I am a really lost about it. I can study how write and run unit test in Objective-C with XCode, but I don't see how useful it is.

In resume, you have to write a method that will be called first to init all thing, and other to finish all things. In the middle you write the test. But it is like to run a normal program. You have access only in what you can have access, like I can't call private function or I didn't see how to do things like:

• If I enter function with X it have to give-me Y

I think it is because I have to fallow the "program rules". I can't see how test the interface things, (like the function one button will run when pressed).

How can I think about the unit test in Objective-C? What I can do and what I can't?