Refs #32508 -- Raised ImproperlyConfigured instead of using "assert" in SessionStorage.

tests/messages_tests/test_session.py

@@ -1,6 +1,7 @@
 from django.contrib.messages import constants
 from django.contrib.messages.storage.base import Message
 from django.contrib.messages.storage.session import SessionStorage
+from django.core.exceptions import ImproperlyConfigured
 from django.http import HttpRequest
 from django.test import TestCase
 from django.utils.safestring import SafeData, mark_safe
@@ -41,7 +42,7 @@ class SessionTests(BaseTests, TestCase):
             'middleware to be installed, and come before the message '
             'middleware in the MIDDLEWARE list.'
         )
-        with self.assertRaisesMessage(AssertionError, msg):
+        with self.assertRaisesMessage(ImproperlyConfigured, msg):
             self.storage_class(HttpRequest())
 
     def test_get(self):