Reverse Engineering

[bonzo5]

I had some poorly documented C++ source code dumped on me that needs to be independently tested (it is display management code).  Using the EA Pro reverse engineering, I got some complicated-looking UML class diagrams (attributes, operations, associations and dependencies).  What is the next logical step?  How would I go from this class diagram to relevant use cases or sequence diagrams, so that I can have test cases to exercise the code?  Any suggestions would be helpful.  I am already grateful that EA Pro lets me start from at least a class diagram.  I just need to understand how to "reverse engineer" that class diagram into sequence diagrams (since other tools allow sequence diagrams to be animated for checking out the code logic).  Thanks to all.