Please feel free to add more unittests, I find writing them is very helpful for finding little bugs and seeing how the interface 'feels'.  Sometimes I find my interface seems too complicated or hard to use by writing a unittest to check it, then I re-write all my code :)  To date, between <code>virsh, libvirt_xml, and libvirt_xml.devices</code> I think I re-wrote each one about three-times before I sent them upstream.  All because writing unittest made me think how to make things simpler & more boring :D