Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Not only about JUnit

When I was learning about JUnit I picked this book and as it turned out, it was pretty good choice. I didn't learn only about JUnit, but also about the core principles of unit testing. Style was very understandable, examples nice, and length was just good enough.It's quite obsolete now and you should be probably looking for JUnit 4.x based book. But if you work with more JUnit 3 based legacy code, it's still pretty good choice.