http://jester.sourceforge.net/

“Why just think your tests are good when you can know for sure?
Sometimes Jester tells me my tests are airtight, but sometimes the
changes it finds come as a bolt out of the blue. Highly recommended.”
Kent Beck

Jester finds code that is not covered by tests. Jester makes some
change to your code, runs your tests, and if the tests pass Jester
displays a message saying what it changed. Jester includes a script
for generating web pages that show the changes made that did not
cause the tests to fail.

E-Mail from Calen Martin D. Legaspi