Good open-source codebase for learning refactoring

What open-source codebases have you used to learn refactoring, written in either java or C# ? One requirement is good unit t开发者_开发技巧ests.

A code that accompanies my "Professional Refactoring in C# ans ASP .NET" book includes a sample application that is refactored throughout the book and you can observe how it evolves. You can download the sample code here. Note: does not include unit tests.