This paper describes the design of the unit testing framework JUnit v3.8. The documentation technique employed is an enhanced version of collaboration-based design, also known as role modeling. In collaboration-based design, objects are viewed as playing multiple roles in different contexts, and different contexts are viewed as task specific collaborations. The documentation accounts for every method in the JUnit 3.8 framework by assigning it to a role. It thereby investigates whether roles and collaborations can serve as basic units of functionality provided by a design like a framework. Such a measure of functionality can serve multiple purposes, for example estimating implementation efforts or measuring complexity.