Fixed #8500 -- Allowed overriding the default admin site instance.

tests/admin_default_site/tests.py

@@ -0,0 +1,31 @@
+from django.contrib import admin
+from django.contrib.admin import sites
+from django.test import SimpleTestCase, override_settings
+
+
+@override_settings(INSTALLED_APPS=[
+    'admin_default_site.apps.MyCustomAdminConfig',
+    'django.contrib.auth',
+    'django.contrib.contenttypes',
+    'django.contrib.sessions',
+    'django.contrib.messages',
+    'django.contrib.staticfiles',
+])
+class CustomAdminSiteTests(SimpleTestCase):
+
+    def setUp(self):
+        # Reset admin.site since it may have already been instantiated by
+        # another test app.
+        self._old_site = admin.site
+        admin.site = sites.site = sites.DefaultAdminSite()
+
+    def tearDown(self):
+        admin.site = sites.site = self._old_site
+
+    def test_use_custom_admin_site(self):
+        self.assertEqual(admin.site.__class__.__name__, 'CustomAdminSite')
+
+
+class DefaultAdminSiteTests(SimpleTestCase):
+    def test_use_default_admin_site(self):
+        self.assertEqual(admin.site.__class__.__name__, 'AdminSite')