[issue32646] test_asyncgen: race condition on test_async_gen_asyncio_gc_aclose_09(), random failure

[STINNER Victor]

New submission from STINNER Victor <victor.stinner at gmail.com>:

test_asyncgen.test_async_gen_asyncio_gc_aclose_09() fails randomly. It looks like a race condition, likely related to the system load.

https://ci.appveyor.com/project/python/cpython/build/3.6build10993/job/l89045et4rmey72q

(...)
Run tests in parallel using 4 child processes
(...)
test_async_gen_asyncio_gc_aclose_09 (test.test_asyncgen.AsyncGenAsyncioTest) ... Task was destroyed but it is pending!
task: <Task pending coro=<async_generator_athrow()> wait_for=<Future finished result=None>>
FAIL

======================================================================
FAIL: test_async_gen_asyncio_gc_aclose_09 (test.test_asyncgen.AsyncGenAsyncioTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\projects\cpython\lib\test\test_asyncgen.py", line 630, in test_async_gen_asyncio_gc_aclose_09
    self.assertEqual(DONE, 1)
AssertionError: 0 != 1
----------------------------------------------------------------------

(...)

Re-running test 'test_asyncgen' in verbose mode
(...)
test_async_gen_asyncio_gc_aclose_09 (test.test_asyncgen.AsyncGenAsyncioTest) ... ok
(...)
Ran 40 tests in 1.125s

----------
components: asyncio
messages: 310580
nosy: asvetlov, vstinner, yselivanov
priority: normal
severity: normal
status: open
title: test_asyncgen: race condition on test_async_gen_asyncio_gc_aclose_09(), random failure
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32646>
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