Working Effectively with Legacy Code

by Michael C. Feathers

this book describes a set of disciplines, concepts, and attitudes that you will carry with you for the rest of your career and that will help you to turn systems that gradually degrade into systems that gradually improve.

legacy code is simply code without tests.

Code without tests is bad code. It doesn’t matter how well written it is; it doesn’t matter how pretty or object-oriented or well-encapsulated it is. With tests, we can change the behavior of our code quickly and verifiably. Without them, we really don’t know if our code is getting better or worse.

I often feel that Extreme Programming is less a way to develop software than it is a way to make a well-jelled work team that just happens to deliver great software every two weeks.