PIT is a code coverage system for Java that goes much further than traditional tools and checks not only that your code is excersied, but that it is actually tested.
PIT achieves this via mutation testing - a technique that has been studied in academia for some time, but has not so far seen widespread commercial use. PIT aims to bring mutation testing into the mainstream of Java development.
The latest release delivers significant performance improvements, running around 200% faster than earlier releases. Also included are support for PowerMock and a number of usability improvements.