What is mutation testing?

Mutation testing is a method for determining how complete your unit tests are. A small mutation is introduced into your code (e.g. a '<' is changed to a '<=') and then your tests are run. If your tests still pass then the code which was changed was (probably) not being completely tested.

How does mutant work?

Given a module, mutant will iterate over all of its top-level functions, modifying their bytecode to introduce mutations and then making sure that the module's doctests fail.

To run:

$ python mutant.py <MODULE-NAME>