Mutant is a mutation tester. It modifies your code and runs your tests to make sure they fail. The idea is that if code can be changed and your tests don't notice, either that code isn't being covered or it doesn't do anything.
mutate "ClassName#method_to_test" spec
To test a class method, use:
mutate "ClassName.class_method_to_test" spec
As an experiment, I've set up a public Trello board with the development roadmap up to the 1.0 release. You can vote and comment cards to give constructive feedback to the project. Just have a look and leave a comment! :)