Jester: Mutation testing for Java
Jester - the JUnit test tester.

			“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.
			
			Jester is different than code coverage tools, because it can
			find code that is executed by the running of tests but not
			actually tested. Jester's approach is called 
			mutation testing
			or automated error seeding. However, Jester is not meant as a replacement for
			code coverage tools, merely as a complementary approach.
			
			Jester is for Java code and JUnit tests (download the latest version of Jester).
 Pester is Jester for
			Python code and PyUnit tests (download Jester version 1.22 and then Pester version 1.01). 
Nester is a port of Jester for C#.
			
			 In general, the latest versions of Jester might require the latest versions of Java/JUnit/Python. Older versions of Jester might work with older versions of Java/JUnit/Python. There
			is absolutely no warranty whatsoever.
			
		