assertTemplateUsed() context manager crashes for templates without names.

[Arian]

When template_names includes at least one None type the string join will fail.
This occurs when a rendered template does not define a name.

Traceback (most recent call last):
  File "/home/.../admin-frontend/admin_frontend/admin_cash/tests/test_views.py", line 19, in test_get_context_data
    with self.assertTemplateUsed('admin_cash/bill_validator_logs.html'):
  File "/home/../3.10/lib/python3.10/site-packages/django/test/testcases.py", line 146, in __exit__
    self.test()
  File "/home/../3.10/lib/python3.10/site-packages/django/test/testcases.py", line 131, in test
    self.test_case._assert_template_used(
  File "/home/../3.10/lib/python3.10/site-packages/django/test/testcases.py", line 828, in _assert_template_used
    % (template_name, ", ".join(template_names)),
TypeError: sequence item 0: expected str instance, NoneType found

​PR

[Arian]

Suggested fix: ​https://github.com/django/django/pull/17237

[Mariusz Felisiak]

Thanks for the report, I was able to reproduce it with the following test:

diff --git a/tests/test_utils/tests.py b/tests/test_utils/tests.py
index cdb0453e44..b0eb0b0f83 100644
--- a/tests/test_utils/tests.py
+++ b/tests/test_utils/tests.py
@@ -547,6 +547,12 @@ class AssertTemplateUsedContextManagerTests(SimpleTestCase):
             response = self.client.get("/test_utils/no_template_used/")
             self.assertTemplateUsed(response, "template_used/base.html")
 
+        with self.assertRaisesMessage(
+            AssertionError, "No templates used to render the response"
+        ):
+            with self.assertTemplateUsed("template_used/base.html"):
+                self.client.get("/test_utils/no_template_used/")
+
     def test_msg_prefix(self):
         msg_prefix = "Prefix"
         msg = f"{msg_prefix}: No templates used to render the response"