Test-Driven Web Development with Python. Very well written and engaging. The prerelease version is available free online at http://chimera.labs.oreilly.com/books/1234000000754. I've known for a long time that I wanted to do unit testing on my web dev projects but never really understood the how part. I'm almost done with the book, and am super excited to try TDD on my projects now.
Test-Driven Web Development with Python
1 reader recommends it across 1 discussion