“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
But I see that there is not even a tag called "Jester" in stackoverflow. So what is the modern replacement for Jester,if any ? How can one be sure that unit tests written are rock solid other than finding statistics from code coverage from tools like Cobertura and Clover?