JUnit in Action by Vincent Massol
JUnit in Action is an example-driven, how-to book about unit testing Java applications (including J2EE applications) using the JUnit framework and its extensions. Intended readers are software architects, developers, testing teams, development managers, Extreme Programmers, or anyone practicing any Agile Methodology.
JUnit in Action is about solving tough real-world problems such as unit testing legacy applications, writing real tests for real objects, automating tests, testing in isolation, unit testing J2EE and database applications, and more.