Refs #19544 -- Added a fast path for through additions if supported.

The single query insertion path is taken if the backend supports inserts
that ignore conflicts and m2m_changed signals don't have to be sent.

1 files changed, 15 insertions, 2 deletions

diff --git a/tests/many_to_many/tests.py b/tests/many_to_many/tests.py
index adde2ac563..098cd29e46 100644
--- a/tests/many_to_many/tests.py
+++ b/tests/many_to_many/tests.py
@@ -118,13 +118,26 @@ class ManyToManyTests(TestCase):
         )
 
     @skipUnlessDBFeature('supports_ignore_conflicts')
-    def test_add_ignore_conflicts(self):
+    def test_fast_add_ignore_conflicts(self):
+        """
+        A single query is necessary to add auto-created through instances if
+        the database backend supports bulk_create(ignore_conflicts) and no
+        m2m_changed signals receivers are connected.
+        """
+        with self.assertNumQueries(1):
+            self.a1.publications.add(self.p1, self.p2)
+
+    @skipUnlessDBFeature('supports_ignore_conflicts')
+    def test_slow_add_ignore_conflicts(self):
         manager_cls = self.a1.publications.__class__
         # Simulate a race condition between the missing ids retrieval and
         # the bulk insertion attempt.
         missing_target_ids = {self.p1.id}
+        # Disable fast-add to test the case where the slow add path is taken.
+        add_plan = (True, False, False)
         with mock.patch.object(manager_cls, '_get_missing_target_ids', return_value=missing_target_ids) as mocked:
-            self.a1.publications.add(self.p1)
+            with mock.patch.object(manager_cls, '_get_add_plan', return_value=add_plan):
+                self.a1.publications.add(self.p1)
         mocked.assert_called_once()
 
     def test_related_sets(self):