gh-136958: fix unittest.TestCase.assertLogs() to properly handle logging.NOTSET level

Author: alex-semenyuk

Lib/test/test_unittest/test_case.py

@@ -1936,6 +1936,35 @@ def testAssertLogsWithFormatter(self):
             self.assertEqual(cm.output, ["[No.1: the larch] INFO:foo:1"])
             self.assertLogRecords(cm.records, [{'name': 'foo'}])
 
+    def testAssertLogsWithNOTSET(self):
+        # Check that logging.NOTSET level is handled correctly
+        # (not treated as falsey and defaulted to INFO)
+        with self.assertNoStderr():
+            with self.assertLogs(level=logging.NOTSET) as cm:
+                log_foo.info("1")
+                log_foobar.debug("2")
+                log_quux.error("3")
+            self.assertEqual(cm.output, ["INFO:foo:1", "DEBUG:foo.bar:2", "ERROR:quux:3"])
+            self.assertLogRecords(cm.records, [
+                {'name': 'foo', 'levelno': logging.INFO},
+                {'name': 'foo.bar', 'levelno': logging.DEBUG},
+                {'name': 'quux', 'levelno': logging.ERROR}
+            ])
+
+    def testAssertNoLogsWithNOTSET(self):
+        # Check that logging.NOTSET level is handled correctly in assertNoLogs
+        # (not treated as falsey and defaulted to INFO)
+        with self.assertNoStderr():
+            with self.assertNoLogs(level=logging.NOTSET):
+                pass
+
+        with self.assertRaises(self.failureException) as cm:
+            with self.assertNoLogs(level=logging.NOTSET):
+                log_foo.debug("debug message")
+
+        self.assertIn("Unexpected logs found", str(cm.exception))
+        self.assertIn("DEBUG:foo:debug message", str(cm.exception))
+
     def testAssertNoLogsDefault(self):
         with self.assertRaises(self.failureException) as cm:
             with self.assertNoLogs():

Lib/unittest/_log.py

@@ -33,7 +33,7 @@ class _AssertLogsContext(_BaseTestCaseContext):
     def __init__(self, test_case, logger_name, level, no_logs, formatter=None):
         _BaseTestCaseContext.__init__(self, test_case)
         self.logger_name = logger_name
-        if level:
+        if level is not None:
             self.level = logging._nameToLevel.get(level, level)
         else:
             self.level = logging.INFO

Misc/NEWS.d/next/Library/2025-08-08-00-55-24.gh-issue-logging-notset.A7bX9z.rst

@@ -0,0 +1,3 @@
+:meth:`unittest.TestCase.assertLogs` and :meth:`unittest.TestCase.assertNoLogs`
+now correctly accept :data:`logging.NOTSET` as a valid level parameter instead
+of treating it as falsey and defaulting to ``logging.INFO``.