Working Effectively with Legacy Code

Chapter 4: The Seam Model

One of the things that nearly everyone notices when they try to write tests for existing code is just how poorly suited code is to testing. It isn’t just particular programs or languages. In general, programming languages just don’t seem to support testing very well. It seems that the only ways to end up with an easily testable program are to write tests as you develop it or spend a bit of time trying to “design for testability.” There is a lot of hope for the former approach, but if much of the code in the field is evidence, the latter hasn’t been very successful.

One thing that I’ve noticed is that, in trying to get code under test, I’ve started to think about code in a rather different way. I could just consider this ...