FYI: since:
commit 23b4b697e5b6cc897696f9c0288c187d2d24bff2
Author: Andrew Svetlov <andrew.svetlov@gmail.com>
Date:   Mon May 27 22:56:22 2019 +0300

    bpo-36889: Merge asyncio streams (GH-13251)



    https://bugs.python.org/issue36889

AIX bot 'hangs' during 
test_sendfile (test.test_asyncio.test_streams.StreamTests)

ctrl-c gives this (in case useful)
Warning -- 'test_asyncio' left behind file '@test_7012552_tmp'
Warning -- asyncio.events._event_loop_policy was modified by test_asyncio
  Before: None
  After:  <asyncio.unix_events._UnixDefaultEventLoopPolicy object at 0x307f8aa8>


== Tests result: INTERRUPTED ==
Test suite interrupted by signal SIGINT.

1 test omitted:
    test_asyncio

Total duration: 13 min 36 sec
Tests result: INTERRUPTED
/data/prj/python/git/python3-3.8/Lib/asyncio/base_events.py:646: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=False>
  _warn(f"unclosed event loop {self!r}", ResourceWarning, source=self)
ResourceWarning: Enable tracemalloc to get the object allocation traceback
Exception ignored in: <coroutine object StreamTests.test_sendfile.<locals>.test at 0x30576ed0>
Traceback (most recent call last):
  File "/data/prj/python/git/python3-3.8/Lib/test/test_asyncio/test_streams.py", line 1643, in test
    await do_connect(*srv.sockets[0].getsockname())
  File "/data/prj/python/git/python3-3.8/Lib/asyncio/streams.py", line 314, in __aexit__
    await self.close()
  File "/data/prj/python/git/python3-3.8/Lib/asyncio/streams.py", line 292, in close
    await tasks.wait([stream.close() for stream in streams])
  File "/data/prj/python/git/python3-3.8/Lib/asyncio/streams.py", line 292, in <listcomp>
    await tasks.wait([stream.close() for stream in streams])
  File "/data/prj/python/git/python3-3.8/Lib/asyncio/streams.py", line 1382, in close
    self._transport.close()
  File "/data/prj/python/git/python3-3.8/Lib/asyncio/selector_events.py", line 680, in close
    self._loop.call_soon(self._call_connection_lost, None)
  File "/data/prj/python/git/python3-3.8/Lib/asyncio/base_events.py", line 711, in call_soon
    self._check_closed()
  File "/data/prj/python/git/python3-3.8/Lib/asyncio/base_events.py", line 504, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed
/data/prj/python/git/python3-3.8/Lib/asyncio/streams.py:352: ResourceWarning: unclosed stream server <StreamServer>
  _warn(f"unclosed stream server {self!r}",
ResourceWarning: Enable tracemalloc to get the object allocation traceback
/data/prj/python/git/python3-3.8/Lib/asyncio/selector_events.py:684: ResourceWarning: unclosed transport <_SelectorSocketTransport fd=7>
  _warn(f"unclosed transport {self!r}", ResourceWarning, source=self)
ResourceWarning: Enable tracemalloc to get the object allocation traceback
/data/prj/python/git/python3-3.8/Lib/asyncio/selector_events.py:684: ResourceWarning: unclosed transport <_SelectorSocketTransport closing fd=8>
  _warn(f"unclosed transport {self!r}", ResourceWarning, source=self)
ResourceWarning: Enable tracemalloc to get the object allocation traceback