Should I write unit test for everything?

Question

I am wondering should I write unit test for everything. There are some classes is very difficult to write unit test. For example, I am writing some program for handling audi

Answer 1

To answer your specific question, use a loopback cable. Connect the speaker out to the mic in. Write a test that renders to the speaker and captures from the mic and verifies that the same thing you played was captured. My suggestion is to use a simple sine tone so that an FFT can tell you if you captured back the same thing.

The answer to the more general question is yes, you should unit test everything you can. Doing so creates a legacy for later so changes down the road can be done with peace of mind. It ensures that your code works as expected. It also documents the intended usage of the interfaces. Finally, it forces better coding style. Usually something which is hard to unit test is also poorly designed. Writing for testability means writing for better design.