investigate random socket binding failures
pydnstest/testserver.py has workaround around line for i in range(self.RETRIES_ON_BIND):
which attempts to work around seemingly random errors:
pydnstest/testserver.py:213: in start_srv
sock.bind(address)
E OSError: [Errno 99] Cannot assign requested address
As far as I can tell it happens only for IPv6, and surprisingly failing addresses were not in use before.
networking.py _add_address() already disables IPv6 Duplicate Address Detection so it should not be a problem.
I've ran out of ideas so the I'm leaving the workaround there for the time being.