0:02:03 load avg: 3.08 [ 26/423] test_asyncio
Unknown child process pid 30234, will report returncode 255
Child watcher got an unexpected pid: 30234
Traceback (most recent call last):
  File "/home/gordon/Images/Python/Python-3.8.0b2/Lib/asyncio/unix_events.py", line 1213, in _do_waitpid
    loop, callback, args = self._callbacks.pop(pid)
KeyError: 30234

(first issue I've logged here, so thanks for your patience!  This system is Debian 9.9 - a 3.7 make was running at the same time but had completed all of the tests before I kicked 3.8 off)

Ran this on a different laptop (Debian 9.9, Lenovo w540) and it passed, so (as I'd expect) this is an intermittent issue.  (The ticket was opened with an error on a Lenovo w510)  Both systems have been reimaged in the last 6-8 months.

0:00:34 load avg: 1.18 [ 26/423] test_asyncio

I got excited prematurely - this is farther down in the log on the second build:

...
0:16:09 load avg: 0.84 [341/423] test_sys_settrace
unhandled exception during asyncio.run() shutdown
task: <Task finished name='Task-4016' coro=<<async_generator_athrow without __name__>()> exception=RuntimeError("can't send non-None value to a just-started coroutine")>
RuntimeError: can't send non-None value to a just-started coroutine
unhandled exception during asyncio.run() shutdown
task: <Task finished name='Task-4019' coro=<<async_generator_athrow without __name__>()> exception=RuntimeError("can't send non-None value to a just-started coroutine")>
RuntimeError: can't send non-None value to a just-started coroutine
0:16:10 load avg: 0.84 [342/423] test_sysconfig
...

The issue title says "test_asyncio fails", but "Unknown child process pid 30234, will report returncode 255" looks more like a warning. Does test_asyncio fail or not?

Please run test_asyncio in verbose mode to identify which test emits the warning.

Without further information, I suggest to just close the issue, since it doesn't sound like a bug, just a warning.

Closing as there isn't enough information and there was no reply to followup questions.  Also 3.8 is no longer maintained. 

Please create a new issue with more information if you are still seeing a problem in a current version of python (3.9+).