Recently, i took ownership of some c++ code. I am going to maintain this code, and add new features later on.
I know many people say that it is usually not worth adding unit-tests to existing code, but i would still like to add some tests which will at least partially cover the code. In particular, i would like to add tests which reproduce bugs which i fixed.
Some of the classes are constructed with some pretty complex state, which can make it more difficult to unit-test.
I am also willing to refactor the code to make it easier to test.
Is there any good article you recommend on guidelines which help to identify classes which are easier to unit-test? Do you have any advice of your own?
While Martin Fowler’s book on refactoring is a treasure trove of information, why not take a look at “Working Effectively with Legacy Code.”
Also, if you’re going to be dealing with classes where there’s a ton of global variables or huge amounts of state transitions I’d put in a lot of integration checks. Separate out as much of the code which interacts with the code you’re refactoring to make sure that all expected inputs in the order they are recieved continue to produce the same outputs. This is critical as it’s very easy to “fix” a subtle bug that might have been addressed somewhere else.
Take notes too. If you do find that there is a bug which another function/class expects and handles properly you’ll want to change both at the same time. That’s difficult unless you keep thorough records.