Meh, I'm not happy to see more @staticmethod where property and devices interface should be used.  Especially since your test already has a VMXML instance it could use.  But I cannot ask you to write the devices.interfaces class.   As a compromise, how about making subclass of VMXML in your test-module, and put these two methods there?  Then I can be happy and pretend they don't exist :)  I will also put on my list to finish out the ``libvirt_xml.devices.interface`` class (the disk class is done).  Good deal?