If you feel like contributing, great! Just fork the repo, make your improvements, and submit a pull request. Tests would, of course, be appreciated. Adding tests where there are no tests currently would be even more appreciated. At least, though, try and not break anything worse than it is. Test coverage has improved, but is still an ongoing concern.
As a reminder, the github page for goiardi is at https://github.com/ctdk/goiardi. Issues can be submitted and reviewed at https://github.com/ctdk/goiardi/issues, and pull requests are at https://github.com/ctdk/goiardi/pulls.
If you feel the need to discuss a contribution, #go-chef on irc.freenode.net is a good place to do so.