[4.2.x] Fixed #34821 -- Prevented DEFAULT_FILE_STORAGE/STATICFILES_STORAGE settings from mutating the main STORAGES.

Regression in 6b965c600054f970bdf94017ecf2e0e6e0a4326b.
Backport of a7c73b944f51d6c92ec876fd7e0a171e7c01657d from main

1 files changed, 12 insertions, 0 deletions

diff --git a/tests/deprecation/test_storages.py b/tests/deprecation/test_storages.py
index 0574f3e880..99a1fc1884 100644
--- a/tests/deprecation/test_storages.py
+++ b/tests/deprecation/test_storages.py
@@ -32,6 +32,7 @@ class StaticfilesStorageDeprecationTests(TestCase):
                 pass
 
     def test_settings_init(self):
+        old_staticfiles_storage = settings.STORAGES.get(STATICFILES_STORAGE_ALIAS)
         settings_module = ModuleType("fake_settings_module")
         settings_module.USE_TZ = True
         settings_module.STATICFILES_STORAGE = (
@@ -49,6 +50,11 @@ class StaticfilesStorageDeprecationTests(TestCase):
                     ),
                 },
             )
+            # settings.STORAGES is not mutated.
+            self.assertEqual(
+                settings.STORAGES.get(STATICFILES_STORAGE_ALIAS),
+                old_staticfiles_storage,
+            )
         finally:
             del sys.modules["fake_settings_module"]
 
@@ -161,6 +167,7 @@ class DefaultStorageDeprecationTests(TestCase):
                 pass
 
     def test_settings_init(self):
+        old_default_storage = settings.STORAGES.get(DEFAULT_STORAGE_ALIAS)
         settings_module = ModuleType("fake_settings_module")
         settings_module.USE_TZ = True
         settings_module.DEFAULT_FILE_STORAGE = "django.core.files.storage.Storage"
@@ -172,6 +179,11 @@ class DefaultStorageDeprecationTests(TestCase):
                 fake_settings.STORAGES[DEFAULT_STORAGE_ALIAS],
                 {"BACKEND": "django.core.files.storage.Storage"},
             )
+            # settings.STORAGES is not mutated.
+            self.assertEqual(
+                settings.STORAGES.get(DEFAULT_STORAGE_ALIAS),
+                old_default_storage,
+            )
         finally:
             del sys.modules["fake_settings_module"]