./python.exe -m test test_types test_inspect fails as (env changed)

[sobolevn]

Bug report

» ./python.exe -m test test_types test_inspect                                  
Using random seed: 1107570136
0:00:00 load avg: 3.01 Run 2 tests sequentially in a single process
0:00:00 load avg: 3.01 [1/2] test_types
0:00:00 load avg: 3.01 [2/2] test_inspect.test_inspect
Warning -- asyncio.events._event_loop_policy was modified by test_inspect.test_inspect
Warning --   Before: None
Warning --   After:  <asyncio.unix_events._UnixDefaultEventLoopPolicy object at 0x102437760> 
test_inspect.test_inspect failed (env changed)

== Tests result: SUCCESS ==

1 test altered the execution environment (env changed):
    test_inspect.test_inspect

1 test OK.

Total duration: 1.0 sec
Total tests: run=473
Total test files: run=2/2 env_changed=1
Result: SUCCESS

I am working on the fix.

Linked PRs

• gh-128694: Fix (env changed) error in test_inspect #128702

[sobolevn]

test_types.py can only contain import unittest.mock to trigger this problem.

[sobolevn]

Because import asyncio is called in import unittest.mock

[sobolevn]

What happens is:

• The first test module imports asyncio and saves it to sys.modules
• This allows self.try_get_module('asyncio') to pass the second time

  cpython/Lib/test/libregrtest/save_env.py

  Lines 95 to 100 in 2fcdc84

  	def get_asyncio_events__event_loop_policy(self):
  	self.try_get_module('asyncio')
  	return support.maybe_get_event_loop_policy()
  	def restore_asyncio_events__event_loop_policy(self, policy):
  	asyncio = self.get_module('asyncio')
  	asyncio._set_event_loop_policy(policy)

• It saves None as the initial value
• Later IsolatedAsyncioTestCase sets the loop policy via Runner:

  cpython/Lib/unittest/async_case.py

  Lines 127 to 142 in 2fcdc84

  	def _setupAsyncioRunner(self):
  	assert self._asyncioRunner is None, 'asyncio runner is already initialized'
  	runner = asyncio.Runner(debug=True, loop_factory=self.loop_factory)
  	self._asyncioRunner = runner
  	def _tearDownAsyncioRunner(self):
  	runner = self._asyncioRunner
  	runner.close()
  	def run(self, result=None):
  	self._setupAsyncioRunner()
  	try:
  	return super().run(result)
  	finally:
  	self._tearDownAsyncioRunner()

• _set_event_loop_policy(None) is never called in tearDown

Ideas?

CC @vstinner

[vstinner]

Tests using IsolatedAsyncioTestCase should call _set_event_loop_policy(None).

[sobolevn]

Yes, that's what I did :)
Thanks!