Mutagen is a plugin to pytest that makes it easy to do mutation
testing. Mutation testing is a method of testing your tests. Mutagen
helps you to define "mutant" versions of your code - code which is
intentionally buggy - then you run your test suite on these mutants
and verify that your tests actually catch the bugs. Mutation testing
helps you to gauge test coverage and verify that your tests are
good enough to exercise interesting behaviors in your code.

WWW: https://pypi.org/project/pytest-mutagen/