One hard part is deciding which code is worth doing mutation testing on. A lot of “business” code probably shouldn’t be tested this way. The effort in writing the tests outweighs the return on investment. But if you’re making shared library code then mutation testing is great. It really gives you confidence that the code is actually working as expected.
If I remember correctly, instead of overwhelming the developer with the full report, CI only presented a hand full of randomly chosen failed mutation tests. The developer then could decide to ignore the result (mutation testing will usually produce some false positives) or extend the tests to kill the mutation.
I used PiTest recently the first time and found it quite useful. As you said, a pretty awesome idea. But definitely not a tool for people who always strive for 100% test coverage.
[1] https://blog.pitest.org/dont-let-your-code-dry/
[2] https://homes.cs.washington.edu/~rjust/publ/mutation_testing...
