[issue32458] test_asyncio failures on Windows

[Antoine Pitrou]

New submission from Antoine Pitrou <pitrou at free.fr>:

It seems test_asyncio fails sporadically on AppVeyor:
https://ci.appveyor.com/project/python/cpython/build/3.7.0a0.10081#L2650

======================================================================
ERROR: test_start_tls_server_1 (test.test_asyncio.test_sslproto.ProactorStartTLS)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\projects\cpython\lib\test\test_asyncio\test_sslproto.py", line 284, in test_start_tls_server_1
    asyncio.wait_for(main(), loop=self.loop, timeout=10))
  File "C:\projects\cpython\lib\asyncio\base_events.py", line 440, in run_until_complete
    return future.result()
  File "C:\projects\cpython\lib\asyncio\tasks.py", line 398, in wait_for
    raise futures.TimeoutError()
concurrent.futures._base.TimeoutError
======================================================================
FAIL: test_start_tls_server_1 (test.test_asyncio.test_sslproto.ProactorStartTLS)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\projects\cpython\lib\test\test_asyncio\functional.py", line 43, in tearDown
    self.fail('unexpected calls to loop.call_exception_handler()')
AssertionError: unexpected calls to loop.call_exception_handler()

----------
components: Library (Lib), Tests
messages: 309244
nosy: asvetlov, giampaolo.rodola, pitrou, yselivanov
priority: normal
severity: normal
status: open
title: test_asyncio failures on Windows
type: behavior
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32458>
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