Growing Object-Oriented Software Guided by Tests, by Steve Freeman and Nat Pryce. The examples are, IIRC, in Java, but the ideas about TDD are applicable to any

Growing Object-Oriented Software Guided by Tests, by Steve Freeman and Nat Pryce. The examples are, IIRC, in Java, but the ideas about TDD are applicable to any OO language. It'll make you think more about how you write testable code and the test themselves.