Async not awaited in some tests. about nbclient

[MSeal]

I'll keep doing some testing on this as I workout changes needed for papermill to continue working as intended. It's possible a different change I made caused the warning in tests to crop up as an execution error.

[MSeal]

Hmm looks like it might be an actual issue when I was testing with papermill (some changes needed to make that work as well):

sys:1: RuntimeWarning: coroutine 'NotebookClient._wait_for_reply' was never awaited
Executing: 100%|████████████████████████████████████████████████████████████████████████████████████████████| 3/3 [01:04<00:00, 10.02s/cell]
Traceback (most recent call last):
  File "/home/mseal/.py3local/bin/papermill", line 11, in <module>
    load_entry_point('papermill', 'console_scripts', 'papermill')()
  File "/home/mseal/.py3local/lib/python3.6/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/home/mseal/.py3local/lib/python3.6/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/home/mseal/.py3local/lib/python3.6/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/mseal/.py3local/lib/python3.6/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/home/mseal/Workspace/papermill/papermill/cli.py", line 235, in papermill
    execution_timeout=execution_timeout,
  File "/home/mseal/Workspace/papermill/papermill/execute.py", line 104, in execute_notebook
    **engine_kwargs
  File "/home/mseal/Workspace/papermill/papermill/engines.py", line 49, in execute_notebook_with_engine
    return self.get_engine(engine_name).execute_notebook(nb, kernel_name, **kwargs)
  File "/home/mseal/Workspace/papermill/papermill/engines.py", line 343, in execute_notebook
    cls.execute_managed_notebook(nb_man, kernel_name, log_output=log_output, **kwargs)
  File "/home/mseal/Workspace/papermill/papermill/engines.py", line 402, in execute_managed_notebook
    return PapermillNotebookClient(nb_man, **final_kwargs).execute()
  File "/home/mseal/Workspace/papermill/papermill/clientwrap.py", line 40, in execute
    self.nb.metadata['language_info'] = info_msg['content']['language_info']
TypeError: 'coroutine' object is not subscriptable
sys:1: RuntimeWarning: coroutine 'NotebookClient._wait_for_reply' was never awaited

[davidbrochart]

The warnings are due to message mocking now being async, which creates coroutines in prepare_cell_mocks. It also appends an idle message to terminate the execute requests, but some tests (e.g. test_eventual_deadline_iopub) don't process all messages on purpose, leaving this last message not awaited.
I'm not sure how we should deal with this, maybe by awaiting the unprocessed messages at the end of the tests, or by having prepare_cell_mocks optionally append the idle message. We could also disable this warning altogether.

[MSeal]

Closing for now, don't think we need to take any action atm