unittests must not rely on any external or default state.  All state/conditions must be known, and this allows you to easily detect if tested 'stuff' is working or not.  In other words, just fudge libvirt_storage.virsh.pool_*() methods so they always return the same, known data.  This way unittest will be predictable and only fail when your code or virsh code interfaces change (i.e. the purpose of unittest :)