Well, without a valid MAC address the function cannot work...

On the other hand, I would not worry too much: uuid._ifconfig_getnode() is an internal function; and since all the other tests pass, uuid.getnode() probably has other ways to get a unique identifier for the machine.

And by the way, in python 3.2, the test function is skipped with this message: 
"""WARNING: uuid._ifconfig_getnode is unreliable on many platforms.
   It is disabled until the code and/or test can be fixed properly."""