“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?

  • I removed my clarifying comment because you edited the question. :) A Google search with that phrase will yield you 3 or 4 examples off the bat, so maybe focus on the conceptual question you have at the end, so you can get some ideas for how best to try out & select the tool that fits your needs?
    – jcmeloni
    Mar 9, 2013 at 16:42
  • @jcmeloni is there any reason why jester didn't really pick up?
    – Geek
    Mar 9, 2013 at 16:44
  • I have no idea; I never used it.
    – jcmeloni
    Mar 9, 2013 at 16:48

1 Answer 1


As far as I'm aware mutation testing remains the best automated process for measuring the quality of your test suite. There are two good modern replacements for jester

http://pitest.org (I'm the author)


A detailed comparison between them, jester, and a couple of other systems is available here


I think the main reason that jester never took off was that it was unworkably slow and scaled very badly.

PIT and javalanche both attempt to address this in a similar way. Instead of blindly running all the tests in a project against a mutation they first gather line coverage and run only those tests that can actually hit a mutation.

PIT also performs various other optimisations to speed things up and offers an option to re-use the results of previous analysis to greatly reduce the computational cost of subsequent runs.

  • The PIT eclipse plugin is not getting installed in Indigo, there seems to be some error in that. Oct 15, 2013 at 12:34
  • @NarendraPathai Try reporting the issue via the pit google group. Phil Glover, who maintains the plugin, might be able to help.
    – henry
    Oct 15, 2013 at 16:20
  • I tried to add the mutation-testing tag to the question, but the tag doesn't exist, and I don't have enough reputation here to do it (at least 300). WDYT of creating the tag yourself @henry? :) Mar 31, 2020 at 7:56
  • @pedrorijo91 done
    – henry
    Mar 31, 2020 at 14:20

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