Goal of this repo is to learn, how mutation testing works, based on PIT framework. Instructions for Maven users are briefly discussed here.
It turns out, that pitest plugin is very picky. If you run this goal in isolation, for example as
in mvn pitest:mutationCoverage, it might happily pass, or utterly fail, depending on some as-yet-unknown state. In
order to achieve any level of reproducibility, I have to always run it as:
mvn clean compile test pitest:mutationCoverage
Couple of words about PIT terminology and configuration:
Killed mutant means "test failed when code was mutated", i.e. this mutation has "mutation coverage" => GOOD.
Survived means "test PASSED" when the code was mutated, i.e. test does not assert for effect of this specific line of
code, meaning this line has no coverage => BAD (for mutation coverage)
No Coverage means "no test has been executed, that would cover this line of code at all" => BAD (for mutation
coverage). For me, this seems to only happen when I run pitest after clean compile goals, but without running test
goal first.
And finally, pitest produces HTML reports under target/pit-reports, which highlight all lines and mutations it tried
to apply.