An overall good and free (!!!) book covering the whole subject of tests from unit tests / TDD to more advanced concept going through other important subjects like test doubles. Each subjects is presented with pragmatic examples.
If you want to discover or review concepts around tests, it's the book to read !
It is a great book with a lot of information not only about TDD itself, but also about different applications. I miss some more depth in some of the chapters with more details about "why" the written statements are true. I have experience with TDD, so I knew many of the things already. In general I can recommend this book to TDD beginner as it contains a lot of exercises as well.
Lot's of great tips and experience in there. It is a must read for any TDD practitioner but I recommend reading it after finishing Kent Beck's TDD by Example.
This is a great companion to the workshops that Jason runs, and provides an opportunity to play back the concepts at your own pace and pick up on subtle points that you might have missed.