Refs #26022 -- Replaced six.assertRaisesRegex with assertRaisesMessage as appropriate.

tests/app_loading/tests.py

@@ -5,7 +5,6 @@ import os
 from django.apps import apps
 from django.test import SimpleTestCase
 from django.test.utils import extend_sys_path
-from django.utils import six
 from django.utils._os import upath
 
 
@@ -57,7 +56,7 @@ class EggLoadingTest(SimpleTestCase):
         """Loading an app from an egg that has an import error in its models module raises that error"""
         egg_name = '%s/brokenapp.egg' % self.egg_dir
         with extend_sys_path(egg_name):
-            with six.assertRaisesRegex(self, ImportError, 'modelz'):
+            with self.assertRaisesMessage(ImportError, 'modelz'):
                 with self.settings(INSTALLED_APPS=['broken_app']):
                     pass