PyMuTester is tool to facilitate Mutant Testing (a.k.a Mutant Analysis or Program Mutation) on software systems written in Python. Its main purpose is to assist you in improving your existing unit tests to cover missing checks and “loopholes” in your testing. It works by making small changes (technically known as mutants) to your Python application’s source code and re-running your unit tests over these mutated applications' source code. Since the mutants usually go against the specifications, your unit tests should fail in such tests. If the unit tests still pass, then that is an indication that your unit tests might have missed some checks.