Backport PR #349: fix testing patch for pyzmq < 17

zmq.COPY_THRESHOLD is undefined prior to pyzmq 17, so we need `create=True` to define it in that case.

Signed-off-by: Min RK <[email protected]>

Author: takluyver

jupyter_client/tests/test_session.py

@@ -41,7 +41,7 @@ def setUp(self):
 @pytest.fixture
 def no_copy_threshold():
     """Disable zero-copy optimizations in pyzmq >= 17"""
-    with mock.patch.object(zmq, 'COPY_THRESHOLD', 1):
+    with mock.patch.object(zmq, 'COPY_THRESHOLD', 1, create=True):
         yield