May 23, 2025 · May 23, 2025
diff --git a/Lib/test/test_unittest/test_case.py b/Lib/test/test_unittest/test_case.py
            with self.assertLogs():
                raise ZeroDivisionError("Unexpected")

    def testAssertLogsWithFormatter(self):
        # Check alternative formats will be respected
        format = "[No.1: the larch] %(levelname)s:%(name)s:%(message)s"
        formatter = logging.Formatter(format)
        with self.assertNoStderr():
            with self.assertLogs() as cm:
                log_foo.info("1")
                log_foobar.debug("2")
            self.assertEqual(cm.output, ["INFO:foo:1"])
            self.assertLogRecords(cm.records, [{'name': 'foo'}])
            with self.assertLogs(formatter=formatter) as cm:
                log_foo.info("1")
                log_foobar.debug("2")
            self.assertEqual(cm.output, ["[No.1: the larch] INFO:foo:1"])
            self.assertLogRecords(cm.records, [{'name': 'foo'}])

    def testAssertNoLogsDefault(self):
        with self.assertRaises(self.failureException) as cm:
            with self.assertNoLogs():
diff --git a/Lib/unittest/_log.py b/Lib/unittest/_log.py

    LOGGING_FORMAT = "%(levelname)s:%(name)s:%(message)s"

    def __init__(self, test_case, logger_name, level, no_logs):
    def __init__(self, test_case, logger_name, level, no_logs, formatter=None):
        _BaseTestCaseContext.__init__(self, test_case)
        self.logger_name = logger_name
        if level:
            self.level = logging.INFO
        self.msg = None
        self.no_logs = no_logs
        self.formatter = formatter

    def __enter__(self):
        if isinstance(self.logger_name, logging.Logger):
            logger = self.logger = self.logger_name
        else:
            logger = self.logger = logging.getLogger(self.logger_name)
        formatter = logging.Formatter(self.LOGGING_FORMAT)
        formatter =self.formatter orlogging.Formatter(self.LOGGING_FORMAT)
        handler = _CapturingHandler()
        handler.setLevel(self.level)
        handler.setFormatter(formatter)
diff --git a/Lib/unittest/case.py b/Lib/unittest/case.py
        context = _AssertNotWarnsContext(expected_warning, self)
        return context.handle('_assertNotWarns', args, kwargs)

    def assertLogs(self, logger=None, level=None):
    def assertLogs(self, logger=None, level=None, formatter=None):
        """Fail unless a log message of level *level* or higher is emitted
        on *logger_name* or its children.  If omitted, *level* defaults to
        INFO and *logger* defaults to the root logger.
        `records` attribute will be a list of the corresponding LogRecord
        objects.

        Optionally supply `format` to control how messages are formatted.

        Example::

            with self.assertLogs('foo', level='INFO') as cm:
        """
        # Lazy import to avoid importing logging if it is not needed.
        from ._log import _AssertLogsContext
        return _AssertLogsContext(self, logger, level, no_logs=False)
        return _AssertLogsContext(self, logger, level, no_logs=False, formatter=formatter)

    def assertNoLogs(self, logger=None, level=None):
        """ Fail unless no log messages of level *level* or higher are emitted
diff --git a/Misc/NEWS.d/next/Tests/2025-05-23-09-19-52.gh-issue-134567.hwEIMb.rst b/Misc/NEWS.d/next/Tests/2025-05-23-09-19-52.gh-issue-134567.hwEIMb.rst
 Expose log formatter to users in TestCase.assertLogs.
 :func:`unittest.TestCase.assertLogs` will now accept a formatter argument so your assertions can match a custom format where you are using one.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1920,6 +1920,22 @@ def testAssertLogsUnexpectedException(self):
		with self.assertLogs():
		raise ZeroDivisionError("Unexpected")

		def testAssertLogsWithFormatter(self):
		# Check alternative formats will be respected
		format = "[No.1: the larch] %(levelname)s:%(name)s:%(message)s"
		formatter = logging.Formatter(format)
		with self.assertNoStderr():
		with self.assertLogs() as cm:
		log_foo.info("1")
		log_foobar.debug("2")
		self.assertEqual(cm.output, ["INFO:foo:1"])
		self.assertLogRecords(cm.records, [{'name': 'foo'}])
		with self.assertLogs(formatter=formatter) as cm:
		log_foo.info("1")
		log_foobar.debug("2")
		self.assertEqual(cm.output, ["[No.1: the larch] INFO:foo:1"])
		self.assertLogRecords(cm.records, [{'name': 'foo'}])

		def testAssertNoLogsDefault(self):
		with self.assertRaises(self.failureException) as cm:
		with self.assertNoLogs():
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -30,7 +30,7 @@ class _AssertLogsContext(_BaseTestCaseContext):

		LOGGING_FORMAT = "%(levelname)s:%(name)s:%(message)s"

		def __init__(self, test_case, logger_name, level, no_logs):
		def __init__(self, test_case, logger_name, level, no_logs, formatter=None):
		_BaseTestCaseContext.__init__(self, test_case)
		self.logger_name = logger_name
		if level:
Expand All		@@ -39,13 +39,14 @@ def __init__(self, test_case, logger_name, level, no_logs):
		self.level = logging.INFO
		self.msg = None
		self.no_logs = no_logs
		self.formatter = formatter

		def __enter__(self):
		if isinstance(self.logger_name, logging.Logger):
		logger = self.logger = self.logger_name
		else:
		logger = self.logger = logging.getLogger(self.logger_name)
		formatter = logging.Formatter(self.LOGGING_FORMAT)
		formatter =self.formatter orlogging.Formatter(self.LOGGING_FORMAT)
		handler = _CapturingHandler()
		handler.setLevel(self.level)
		handler.setFormatter(formatter)
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -851,7 +851,7 @@ def _assertNotWarns(self, expected_warning, args, *kwargs):
		context = _AssertNotWarnsContext(expected_warning, self)
		return context.handle('_assertNotWarns', args, kwargs)

		def assertLogs(self, logger=None, level=None):
		def assertLogs(self, logger=None, level=None, formatter=None):
		"""Fail unless a log message of level level or higher is emitted
		on logger_name or its children. If omitted, level defaults to
		INFO and logger defaults to the root logger.
Expand All		@@ -863,6 +863,8 @@ def assertLogs(self, logger=None, level=None):
		`records` attribute will be a list of the corresponding LogRecord
		objects.

		Optionally supply `format` to control how messages are formatted.

		Example::

		with self.assertLogs('foo', level='INFO') as cm:
Expand All		@@ -873,7 +875,7 @@ def assertLogs(self, logger=None, level=None):
		"""
		# Lazy import to avoid importing logging if it is not needed.
		from ._log import _AssertLogsContext
		return _AssertLogsContext(self, logger, level, no_logs=False)
		return _AssertLogsContext(self, logger, level, no_logs=False, formatter=formatter)

		def assertNoLogs(self, logger=None, level=None):
		""" Fail unless no log messages of level level or higher are emitted
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Expose log formatter to users in TestCase.assertLogs.
		:func:`unittest.TestCase.assertLogs` will now accept a formatter argument so your assertions can match a custom format where you are using one.