Example of failure:

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ERROR: setUpClass (test.test_nntplib.NetworkedNNTPTests)
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Traceback (most recent call last):
  File "/home/haypo/prog/python/master/Lib/test/test_nntplib.py", line 289, in setUpClass
    cls.server = cls.NNTP_CLASS(cls.NNTP_HOST, timeout=TIMEOUT, usenetrc=False)
  File "/home/haypo/prog/python/master/Lib/nntplib.py", line 1048, in __init__
    readermode, timeout)
  File "/home/haypo/prog/python/master/Lib/nntplib.py", line 330, in __init__
    self.welcome = self._getresp()
  File "/home/haypo/prog/python/master/Lib/nntplib.py", line 449, in _getresp
    resp = self._getline()
  File "/home/haypo/prog/python/master/Lib/nntplib.py", line 437, in _getline
    if not line: raise EOFError
EOFError

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Attached PR catch this error and skips the test.

See also issue #19613 and #19756.