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

Use unit testing where it makes sense - don't aim for 100% coverage. The main guideline is to think rather than applying either dogma or laziness.

Having said that: If you have classes which are naturally hard to test, try to reduce how much they have to do. Isolate the untestable code and separate its API into an interface. Then test the logic which uses that API against a mock or stub.