diff --git a/ballista/rust/core/src/serde/mod.rs b/ballista/rust/core/src/serde/mod.rs
index 3a1736c9fa3e..49d2b47ba6c7 100644
--- a/ballista/rust/core/src/serde/mod.rs
+++ b/ballista/rust/core/src/serde/mod.rs
@@ -775,6 +775,12 @@ mod tests {
             // better statistics inference could be provided
             Statistics::default()
         }
+
+        fn output_ordering(
+            &self,
+        ) -> Option<&[datafusion::physical_plan::expressions::PhysicalSortExpr]> {
+            todo!()
+        }
     }
 
     struct TopKPlanner {}