> Without the test we would have missed some of the required changes 

Then I think we should write tests to verify those changes. In other words, have the tests verify the contract that your subclass is expecting. 

@reinholdfuereder 

> I personally think that tests are often the best type of documentation.

I agree, but we need to make sure that the tests are maintainable, and that it's clear what's being tested (so if a  refactoring breaks a test, we can tell if the problem is with the refactoring or with the test). I like tests, too. I think what you have here is bigger than it needs to be, that's all.