Good literature on unit testing?

Growing Object-Oriented Software Guided by Tests

xUnit Test Patterns: Refactoring Test Code

The real challenge of software testing is solving the puzzle of test design.

Testing Object-Oriented Systems: Models, Patterns, and Tools provides three dozen test design patterns applicable to unit test design. It also provides many design patterns for test automation. These patterns distill many hard-won best practices and research insights.

The book is designed as a desk reference, so once you've determined which patterns fit your app, you only need to read about them. Because of this, it is a big book (1024 pages). I know, because I am the author.

Overview, reviews, and link to Amazon: http://www.robertvbinder.com/home/thought-leadership/books/

The Art Of Unit Testing