I wonder if in the future we'd be better served as this being a groupmod provider that builds on the groupadd provider. This then makes me wonder why the groupadd provider specifically lacked groupmod support. Do we know of an operating system or distribution that has groupadd but not groupmod?
This decision can be left until the future when we want to support such a system, at which point we could refactor the providers.
Merged to opscode/master.
Thanks for the contribution!