Add FIXME to test_msc4242

tests/storage/test_msc4242_state_dag.py

@@ -155,6 +155,9 @@ class MSC4242EventPersistenceStateDagsStoreTestCase(HomeserverTestCase):
         rejected: bool = False,
     ) -> tuple[MSC4242Event, EventContext]:
         # We use a mock here to allow us to set the `event_id`.
+        #
+        # FIXME: It would be better to use a real event here, but that is more
+        # complex to set up.
         ev = Mock(spec=EventBase)
         ev.event_id = id
         ev.prev_state_events = prev_state_events