Unable to use `logging.NOTSET` with `assertLogs` or `assertNoLogs`

Bug report

Bug description:

Since logging.NOTSET equals 0 (a falsey value), the naive conditional check in _AssertLogsContext prevents it from being used as a valid level parameter with unittest.TestCase.assertLogs() or unittest.TestCase.assertNoLogs().

Example:

import logging
import unittest


class LoggerTestCase(unittest.TestCase):
    def test_logging(self):
        root_logger = logging.getLogger()
        root_logger.setLevel(logging.ERROR)

        logger = logging.getLogger("foo")

        with self.assertLogs(logger=logger, level=logging.NOTSET) as cm:
            logger.info("first message")
            logger.error("second message")
            # This test currently fails because `assertLogs(...)` sees the falsey
            # `logging.NOTSET` and sets the level to `logging.INFO` by default; so we
            # end up seeing the "INFO:foo:first message" in the output.
            self.assertEqual(cm.output, ["ERROR:foo:second message"])

In my real life use case, the logging.NOTSET interaction is useful in context of creating a custom class ExplicitlyConfiguredLogger(logging.Logger) that only logs when the logger is configured with something other than logging.NOTSET (used in https://github.com/element-hq/synapse/pull/18474) and wanting to write some tests for it.

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-137555

Comece em Lib/unittest/_log.py, na condição de _AssertLogsContext referenciada na issue. Reproduza o exemplo com logging.NOTSET por meio de assertLogs e assertNoLogs e, em seguida, verifique se ambos os contextos aceitam o nível sem usar INFO como padrão e se a cobertura de regressão exercita esse comportamento.