This will break if libvirt is not installed on the machine running the unit test.  However, unittest is about libvirt_storage module and not virsh module, so tests must still run.  You will need to use mock (<code>autotest/client/shared/test_utils/mock*</code>) to "simulate" the virsh module for purpose of these unittest.  Alternatively, you can "cheat" and just re-define the parts of <code>libvirt_storage.virsh.Virsh</code> to be a dummy methods, similar to how <code>libvirt_xml_unittest.py<code> does in <code>LibvirtXMLTestBase.setUp()</code>.  Please copy this pattern if it is easier than mock.