Too Long; Didn't Read
There are two different approaches when writing unit test-cases is concerned: You follow a Test Driven Development and then, later on, develop your code from there. The TDD approach originated during the early stage of Agile development, most probably in the early 2000s. This is where our second point comes into the picture. You write test-case to make your product mature. You will be aware of any faulty code that has entered your codebase. Be negative with your test class. Don’t go looking for a test cause a problem, that’s correct.