Unit tests for JTidy

Hello,

I'm a student (Wroclaw University of Technology). We have a course about
unit test. We have to choose some existing project and write some unit test
for it. We chose JTidy. Could you tell me please some advice. What to test.
I found the newest source code with some test. Now I have to write more
test. I use eclipse witch JUnit and plugin Emma for code coverage.

Thanks for reply
Chris