Yes, ``libvirt_xml_unittest`` is getting a bit too-big, I agree with separating some tests, good idea.  The filename seems a bit strange to me, would it be more clear as ``libvirt_xml_network_unittest``?  If maybe you are planning on moving more non-network unittests here, then forget it.  Just an option to consider since it is only my opinion about name, not a big deal.