Fixed #30027 -- Errored out on Window function usage if unsupported.

1 files changed, 7 insertions, 1 deletions

diff --git a/tests/expressions_window/tests.py b/tests/expressions_window/tests.py
index fa9bb2916b..a993a5e575 100644
--- a/tests/expressions_window/tests.py
+++ b/tests/expressions_window/tests.py
@@ -1,5 +1,5 @@
 import datetime
-from unittest import skipIf, skipUnless
+from unittest import mock, skipIf, skipUnless
 
 from django.core.exceptions import FieldError
 from django.db import NotSupportedError, connection
@@ -821,6 +821,12 @@ class NonQueryWindowTests(SimpleTestCase):
         with self.assertRaisesMessage(NotSupportedError, msg):
             Employee.objects.annotate(dense_rank=Window(expression=DenseRank())).filter(dense_rank__gte=1)
 
+    def test_unsupported_backend(self):
+        msg = 'This backend does not support window expressions.'
+        with mock.patch.object(connection.features, 'supports_over_clause', False):
+            with self.assertRaisesMessage(NotSupportedError, msg):
+                Employee.objects.annotate(dense_rank=Window(expression=DenseRank())).get()
+
     def test_invalid_order_by(self):
         msg = 'order_by must be either an Expression or a sequence of expressions'
         with self.assertRaisesMessage(ValueError, msg):