Add tests.
Add a mock to return users with groups.
Squashed commit of the following:

commit 60417dc468b3621bae0729e88ca992615e59aebf
Author: Alexis Mineaud <alexis@gandi.net>
Date:   Fri Jan 31 11:09:50 2014 +0100

    Several fixes to make all stuff working.

commit 77d68ce668dd0239218c825cadeafd74aaba2bb8
Author: Alexis Mineaud <alexis@gandi.net>
Date:   Thu Jan 30 18:27:16 2014 +0100

    Hum, dealing with modules loading...