EasyWFUnit is an extension to the library-based unit-testing facilities in Microsoft Visual Studio 2008 as well as NUnit. EasyWFUnit provides a framework to write unit tests against Workflow objects. Using the base classes provided, you can define asserts to determine whether particular paths were taken during Workflow execution, and whether activities -- including custom activities -- execute as expected.
EasyWFUnit was written targeting the .NET Framework version 3.5. Full source for Visual Studio 2008 is provided.