Refs #35667 -- Cached Django file prefixes for warnings.

tests/deprecation/tests.py

@@ -1,7 +1,32 @@
+import os
 import warnings
 
+import django
 from django.test import SimpleTestCase
-from django.utils.deprecation import RemovedAfterNextVersionWarning, RenameMethodsBase
+from django.utils.deprecation import (
+    RemovedAfterNextVersionWarning,
+    RenameMethodsBase,
+    django_file_prefixes,
+)
+
+
+class DjangoFilePrefixesTests(SimpleTestCase):
+    def setUp(self):
+        django_file_prefixes.cache_clear()
+
+    def test_no_file(self):
+        orig_file = django.__file__
+        try:
+            del django.__file__
+            self.assertEqual(django_file_prefixes(), ())
+        finally:
+            django.__file__ = orig_file
+
+    def test_with_file(self):
+        prefixes = django_file_prefixes()
+        self.assertIsInstance(prefixes, tuple)
+        self.assertEqual(len(prefixes), 1)
+        self.assertTrue(prefixes[0].endswith(f"{os.path.sep}django"))
 
 
 class RenameManagerMethods(RenameMethodsBase):