Wicket, a lightweight, component-oriented web application framework in plain Java and XHTML, stresses separation of concerns, testability, and good object-oriented design practices. Check out Wicket's approach to common implementation scenarios.
Unitils is an open source testing framework for Java that dramatically reduces boilerplate test code. Test-driven design is a test-first methodology that uses programmatic tests as design tools. Find out how to realize the benefits of test-driven design using Unitils.