Working Effectively with Legacy Code

This book contains a number of practical techniques for dealing with legacy code, ie code lacking sufficient test coverage. In particular it has a lot of approaches for breaking dependencies so that you can get a single unit of functionality under test.

I found that I had already been exposed to a number of techniques in the book, however this is not something I hold against. The techniques solve real problems encountered in day to day development and were quite possibly picked up from colleagues who had previously read this.

Hopefully modern code will be written in such a way that you dont need to use any of these techniques, but it useful to have them in your toolbox and know you can refer back to it on that day you get tasked with making changes to a legacy system.