title: code mutator for Ruby other than heckle?
body: <p>I am working with ruby 1.8, rails 3.1 and rspec 2.7</p>
  
  <p>I am trying to make very good tests, I want to try one of those code mutation tools. I have only found Heckle but it seems to be very outdated and I am having a hard time to make it work with my setup.<br>
  Is there any other code mutation tool for Ruby out there? 
  or 
  Is there any other way get some automatic feedback on the quality of tests? (excluding coverage)</p>