"Four human beings -- changed by space-born cosmic rays into something more than merely human."
— The Fantastic Four

Cosmic Ray is a tool for performing mutation testing on Python code.

At this time Cosmic Ray is young and incomplete. It doesn't support all of the mutations it should, its output format is crude, it only supports some forms of test discovery, it may fall over on exotic modules...the list goes on and on. Still, for the adventurous it does work. Hopefully things will improve fairly rapidly.

And, of course, patches and ideas are welcome.

If you just want to get down to the business of finding and killing mutants, here's what you do:

pip install cosmic_ray
cosmic-ray run --baseline=2 my_module path/to/tests

This will print out a bunch of information about what Cosmic Ray is doing, including stuff about what kinds of mutants are being created, which were killed, and – chillingly – which survived.

Further documentation is available at readthedocs.