Is it OK to copy & paste unit-tests when the logic is basically the same?

Question

I currently have like 10 tests that test whenever my Tetris piece doesn\'t move left if there is a piece in the path, or a wall. Now, I will have to test the same behaviour for

Answer 1

I have a somewhat controversial position on this one. While code duplication must be avoided as much as possible in production code, this is not so bad for test code. Production and test code differ in nature and intent:

• Production code can afford some complexity so as to be understandable/maintainable. You want the code to be at the right abstraction level, and the design to be consistent. This is ok because you have tests for it and you can make sure it works. Code duplication in production code wouldn't be a problem if you had really a 100% code coverage at the logical level. This is really hard to achieve, so the rule is: avoid duplication and maximize code coverage.

• Test code on the other hand must be as simple as possible. You must make sure that test code actually tests what it should. If tests are complicated, you might end up with bug in the tests or the wrong tests -- and you don't have tests for the tests, so the rule is: keep it simple. If test code is duplicated, this is not so a big problem when it something changes. If the change is applied only in one test, the other will fail until you fix it.

The main point I want to make is that production and test code have a different nature. Then it's always a matter of common sense, and I'm not saying you should not factor test code, etc. If you can factor something in test code and you're sure it's ok, then do it. But for test code, I would favor simplicity over elegance, while for production code, I would favor elegance over simplicity. The optimum is of course to have a simple, elegant solution :)

PS: If you really don't agree, please leave a comment.