Py3.7 test failure MismatchError: 'info\nwarn\n' != 'warn\n'

[Corey Bryant]

The following test is failing with Py3.7:

FAIL: oslo_log.tests.unit.test_log.MutateTestCase.test_remove_logger
--------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/corey/pkg/rocky2/upstream/oslo.log/oslo_log/tests/unit/test_log.py", line 1544, in test_remove_logger
    self.assertEqual("info\nwarn\n", stream.getvalue())
  File "/home/corey/pkg/rocky2/upstream/oslo.log/.tox/py37/lib/python3.7/site-packages/testtools/testcase.py", line 411, in assertEqual
    self.assertThat(observed, matcher, message)
  File "/home/corey/pkg/rocky2/upstream/oslo.log/.tox/py37/lib/python3.7/site-packages/testtools/testcase.py", line 498, in assertThat
    raise mismatch_error
testtools.matchers._impl.MismatchError: 'info\nwarn\n' != 'warn\n'
Ran 178 tests in 7.423s
FAILED (id=0, failures=3, skips=1)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/676450

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/676450
Committed: https://git.openstack.org/cgit/openstack/oslo.log/commit/?id=500788981e1abcd5a495badac350285e39f993a4
Submitter: Zuul
Branch: master

commit 500788981e1abcd5a495badac350285e39f993a4
Author: Ben Nemec <email address hidden>
Date: Wed Aug 14 16:02:23 2019 +0000

    Use setLevel instead of setting logger.level directly

    Python 3.7 added caching of the log level for calls to isEnabledFor
    on a logger[0]. As a result, modifying the logger level directly
    can cause a mismatch in behavior if a log call was made prior to
    that modification. In our case, we were calling logger.info before
    the info level was enabled, which meant the logger cached the fact
    that it was not enabled for info-level logging. Even after setting
    the level to NOTSET, it was still remembering that it shouldn't log
    info messages and that breaks our unit tests on py37. There is a
    related issue open against Python[1], but basically the answer there
    was "don't mess with logger internals".

    The simple fix is to use logger.setLevel for resetting the log level
    instead of modifying the attribute directly.

    Change-Id: Ifd1300d8e4280df1913f632e964f9458dbb2db55
    0: https://github.com/python/cpython/commit/78c18a9b9a1445f7c755929917a790ba02b4a5e0#diff-5bd69232a06838f179312d3e48ccf506
    1: https://bugs.python.org/issue34269
    Closes-Bug: 1783630

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/oslo.log 3.44.1 release.