The following test code unexpectedly passes.

import logging
import unittest

LOG_FORMAT = '%(levelname)-10s %(asctime)s: %(message)s'


def set_up_logger(app_name, level=logging.INFO, file="test.log"):
    formatter = logging.Formatter(LOG_FORMAT)
    log = logging.getLogger(app_name)
    # The next line lets the test pass
    log.setLevel(level)
    return log

logger = set_up_logger(__name__)

class TestLogging(unittest.TestCase):
    def test_logging(self):
        with self.assertLogs(level=logging.WARNING):
            logger.info('foo')

Based on discussion at https://stackoverflow.com/questions/64141681/any-level-of-logging-lets-assertlogs-pass, it appears that I need to pass in the logger which is going to be doing the logging.  

Doing so would make the test over-specific and fragile.  The requirement is that a warning be logged, not that a specific logger issue the warning.

This was verified with Python 3.8.5 on a Mac, but probably exists in most/all other versions.

You didn't specify the logger in the assertLogs() call. 

The documentation says that "The default is the root logger, which will catch all messages."

https://docs.python.org/3/library/unittest.html#unittest.TestCase.assertLogs

This is behaving as expected.

New changeset 1ed54435268b285964141fb74d47ceaa33ea79ab by Irit Katriel in branch 'master':
bpo-41898: add caveat on root logger seeing all messages in assertLogs doc (GH-22526)
https://github.com/python/cpython/commit/1ed54435268b285964141fb74d47ceaa33ea79ab

New changeset b2611fac05ed391d68f09781903aae7394fab832 by Miss Skeleton (bot) in branch '3.8':
bpo-41898: add caveat on root logger seeing all messages in assertLogs doc (GH-22526) (GH-22537)
https://github.com/python/cpython/commit/b2611fac05ed391d68f09781903aae7394fab832

New changeset faa8c6a8f1fe9c3bac31061e8a59a686b983ebb8 by Miss Skeleton (bot) in branch '3.9':
bpo-41898: add caveat on root logger seeing all messages in assertLogs doc (GH-22526) (GH-22540)
https://github.com/python/cpython/commit/faa8c6a8f1fe9c3bac31061e8a59a686b983ebb8

I'm not sure my patch completely resolved this issue. I'm adding Antoine re the OP's question about the assertLogs API. 

> Doing so would make the test over-specific and fragile.  The requirement is > that a warning be logged, not that a specific logger issue the warning.

My view is that your test is fragile because it just asks "was anything logged" without checking the log message. The docs show how to verify that the log message is what you expect it to be.

Troy, 

I'm also confused about how you would have liked assertLogs to behave you say:

1. I don't want to specify the logger because I don't care which logger the message comes from.

2. I don't want it to catch messages from other loggers (whatever other means here).  But -- see 1 -- you didn't specify the logger because you don't care which logger.

What do you expect assertLogs to do when you don't specify a logger?

Please reopen this issue. I understand after a discussion on stackoverflow what the problem is, and there is indeed a bug. I will create a PR with a unit test for it an a fix.

Strike that - Troy has created the new issue 41943 so this one can remain closed.