PIT is a fast bytecode based mutation testing system for Java that makes it possible to test the effectiveness of your unit tests. You can think of mutation testing as either as an automated test of your tests or as a much more in-depth form of code coverage. Unlike traditional line and branch coverage tools, PIT does not just confirm that your tests execute your code, it confirms that your tests are actually able to detect faults in it.
This release includes support for TestNG, an important defect fix for incorrect behavior when mutating nested classes, console statistics, and improved handling of the classpath.
URL: PIT mutation testing