Add a test to ensure display name changes don't generate extra room_joined profile updates rows, due to membership event changes

tests/handlers/test_profile.py

@@ -582,6 +582,80 @@ class ProfileTestCase(unittest.HomeserverTestCase):
             ],
         )
 
+    @override_config({"include_profile_updates_in_sync": True})
+    def test_display_name_change_does_not_generate_join_action_rows_for_profile_updates(
+        self,
+    ) -> None:
+        """Test that changing ones display name doesn't generate "joined_room"
+        profile updates to the stream, due to room state membership event changes,
+        if MSC4429 is enabled.
+        """
+        self.register_user("roger", "password")
+        roger_token = self.login("roger", "password")
+        room_id = self.helper.create_room_as(
+            room_creator=self.frank.to_string(),
+            tok=self.frank_token,
+        )
+        self.helper.join(room_id, "@roger:test", tok=roger_token)
+        per_user_updates = self.get_success(
+            self.store.get_profile_updates_for_user_and_fields(
+                from_id=0,
+                to_id=10,
+                user_id=self.frank.to_string(),
+                field_names={"displayname"},
+            )
+        )
+        # Starting situation
+        self.assertEqual(
+            per_user_updates,
+            [
+                ProfileUpdate(
+                    stream_id=2,
+                    user_id="@roger:test",
+                    action="joined_room",
+                    field_name=None,
+                ),
+            ],
+        )
+
+        # Change rogers display name
+        self.get_success(
+            self.handler.set_field(
+                target_user=UserID.from_string("@roger:test"),
+                requester=synapse.types.create_requester("@roger:test"),
+                field_name="displayname",
+                new_value="Roger new name",
+            )
+        )
+
+        per_user_updates = self.get_success(
+            self.store.get_profile_updates_for_user_and_fields(
+                from_id=0,
+                to_id=10,
+                user_id=self.frank.to_string(),
+                field_names={"displayname"},
+            )
+        )
+        # Only the displayname change should appear, no extra "room join" due to
+        # membership state event changes.
+        self.assertEqual(
+            per_user_updates,
+            [
+                ProfileUpdate(
+                    stream_id=2,
+                    user_id="@roger:test",
+                    action="joined_room",
+                    field_name=None,
+                ),
+                ProfileUpdate(
+                    stream_id=3,
+                    user_id="@roger:test",
+                    action="update",
+                    field_name="displayname",
+                ),
+            ],
+        )
+
     @parameterized.expand(
         [
             ["displayname", "Frank"],