https://ci.appveyor.com/project/python/cpython/builds/24376676

ERROR: test_drain_raises (test.test_asyncio.test_streams.StreamTests)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "C:\projects\cpython\lib\test\test_asyncio\test_streams.py", line 820, in test_drain_raises
    self.loop.run_until_complete(client(*addr))
  File "C:\projects\cpython\lib\asyncio\base_events.py", line 584, in run_until_complete
    return future.result()
  File "C:\projects\cpython\lib\test\test_asyncio\test_streams.py", line 810, in client
    await writer.drain()
  File "C:\projects\cpython\lib\asyncio\streams.py", line 351, in drain
    await fut
  File "C:\projects\cpython\lib\asyncio\selector_events.py", line 860, in write
    n = self._sock.send(data)
ConnectionAbortedError: [WinError 10053] An established connection was aborted by the software in your host machine

I have gotten this too, multiple times, on both Azure Pipelines and Appveyor. The latter is worse since required. There was also a Mac failure for Azure, not sure is same issue.

Please disable this test. External resource problems should not be blocking merges of good patches. This is especially obnoxious for backports because it is not possible to rerun by close and reopen, as closing causes the backport branch to be deleted.

Maybe the test started to fail randomly after this change:

commit 1cc0ee7
Author: Andrew Svetlov <andrew.svetlov@gmail.com>
Date: Tue May 7 16:53:19 2019 -0400

bpo-36801: Fix waiting in StreamWriter.drain for closing
SSL transport (GH-13098)

The test is quite old, added in bpo-25441:

commit c44ecdf
Author: Guido van Rossum <guido@python.org>
Date: Mon Oct 19 11:49:30 2015 -0700

Issue bpo-25441: asyncio: Raise error from drain() when socket is closed.

Another candidate:

commit a076e4f (refs/bisect/bad)
Author: Andrew Svetlov <andrew.svetlov@gmail.com>
Date: Thu May 9 15:14:58 2019 -0400

bpo-36802: Drop awrite()/aclose(), support await write() and await close() instead (bpo-13099)

Before this commit, the test pass. After this commit, the test still pass but logs a warning:

vstinner@WIN C:\vstinner\python\master>python -m test test_asyncio -m test_drain_raises -v
(...)
test_drain_raises (test.test_asyncio.test_streams.StreamTests) ... Task exception was never retrieved
future: <Task finished name='Task-2' coro=<StreamWriter.drain() done, defined at C:\vstinner\python\master\lib\asyncio\streams.py:417> exception=ConnectionAbor
tedError(10053, 'An established connection was aborted by the software in your host machine', None, 10053, None)>
Traceback (most recent call last):
  File "C:\vstinner\python\master\lib\asyncio\streams.py", line 434, in drain
    await fut
  File "C:\vstinner\python\master\lib\asyncio\proactor_events.py", line 370, in _loop_writing
    self._write_fut = self._loop._proactor.send(self._sock, data)
  File "C:\vstinner\python\master\lib\asyncio\windows_events.py", line 488, in send
    ov.WSASend(conn.fileno(), buf, flags)
ConnectionAbortedError: [WinError 10053] An established connection was aborted by the software in your host machine
ok
(...)
Tests result: SUCCESS

I wrote PR 13316 to revert the commit a076e4f of bpo-36802:
https://bugs.python.org/issue36802#msg342471

Please postpone the reversion for a while.
I think bpo-36916 fixes a message about the never retrieved exception.

PR 13313 has been merged into master. Let's see if it does fix this issue in master.

Python 3.7 is different: streams.py doesn't have _fast_drain() which was added by commit a076e4f (bpo-36802). So instead, I created PR 13328 to revert the commit 93aa57a of bpo-36801, to get more time to find a proper fix to Python 3.7.

Agree with your conclusion

"""
commit 1cc0ee7
Author: Andrew Svetlov <andrew.svetlov@gmail.com>
Date: Tue May 7 16:53:19 2019 -0400

bpo-36801: Fix waiting in StreamWriter.drain for closing
SSL transport (GH-13098)

"""

I reverted this change in 3.7:

commit c647ad9 (HEAD -> 3.7, upstream/3.7)
Author: Victor Stinner <victor.stinner@gmail.com>
Date: Tue May 14 22:29:54 2019 +0200

Revert "bpo-36801: Fix waiting in StreamWriter.drain for closing SSL transport (GH-13098)" (GH-13328)

This reverts commit 93aa57ac6594d1cc30d147720fc8a7a4e1ca2d3e.

Without this revert, I was able to easily reproduce the failure. With the revert, I cannot reproduce it anymore:
#13328 (comment)

Andrew merged #13330 into master, it should fix this issue.