The check_node() function in test_uuid.py uses the wrong bitmask, causing the tests to fail on valid MAC addresses.  Also, the description in the comment is incorrect.  From my reading of the wikipedia page, the test is trying to ensure that the MAC address is "universally administered", which is designated by a zero value in "the second least significant digit of the first octet".

Thus the bitmask value *and* the comment are both wrong AFAICT, given that the original value is:

% ./python.exe -c "from math import log2; print(log2(0x010000000000))"
40.0

I have a fix that passes on my machine, so I'll PR that and see if it passes on CI.