Investigate test failure when running with Notebook 6.1.6

[kevin-bates]

pytest enterprise_gateway/tests/test_handlers.py fails with the following output when running against Notebook 6.1.6 and is likely related to jupyter/notebook#5908...

$ pytest enterprise_gateway/tests/test_handlers.py 
=============================================================================== test session starts ================================================================================
platform darwin -- Python 3.8.5, pytest-6.1.0, py-1.9.0, pluggy-0.13.1
rootdir: /Users/kbates/repos/oss/jupyter/enterprise_gateway
plugins: tornasync-0.6.0.post2, console-scripts-1.1.0, jupyter-0.0.1, shutil-1.7.0, jupyterlab-3.0.0rc10, virtualenv-1.7.0, jupyter-server-1.0.7, jupyterlab-server-2.0.0rc3
collected 23 items                                                                                                                                                                 

enterprise_gateway/tests/test_handlers.py ...........F...........                                                                                                            [100%]

===================================================================================== FAILURES =====================================================================================
__________________________________________________________________________ TestDefaults.test_kernel_comm ___________________________________________________________________________

self = <enterprise_gateway.tests.test_handlers.TestDefaults testMethod=test_kernel_comm>

    @gen_test
    def test_kernel_comm(self):
        """Default kernel should launch and accept commands."""
        ws = yield self.spawn_kernel()
    
        # Send a request for kernel info
        ws.write_message(json_encode({
            'header': {
                'username': '',
                'version': '5.0',
                'session': '',
                'msg_id': 'fake-msg-id',
                'msg_type': 'kernel_info_request'
            },
            'parent_header': {},
            'channel': 'shell',
            'content': {},
            'metadata': {},
            'buffers': {}
        }))
    
        # Assert the reply comes back. Test will timeout if this hangs.
        for _ in range(3):
            msg = yield ws.read_message()
            msg = json_decode(msg)
            if(msg['msg_type'] == 'kernel_info_reply'):
                break
        else:
>           self.assertTrue(False, 'never received kernel_info_reply')
E           AssertionError: False is not true : never received kernel_info_reply

enterprise_gateway/tests/test_handlers.py:404: AssertionError