bpo-39259: nntplib.NNTP/NNTP_SSL now reject timeout = 0 (GH-17936)

nntplib.NNTP and nntplib.NNTP_SSL now raise a ValueError
if the given timeout for their constructor is zero to
prevent the creation of a non-blocking socket.

Lib/test/test_nntplib.py

@@ -258,6 +258,10 @@ class NetworkedNNTPTestsMixin:
             # value
             setattr(cls, name, wrap_meth(meth))
 
+    def test_timeout(self):
+        with self.assertRaises(ValueError):
+            self.NNTP_CLASS(self.NNTP_HOST, timeout=0, usenetrc=False)
+
     def test_with_statement(self):
         def is_connected():
             if not hasattr(server, 'file'):