First stab at fixing the error, not a full success.

src/renderer/renderer.rs

@@ -520,6 +520,11 @@ mod tests {
         fn equals(&self, other: &dyn ContextElement) -> bool {
             false
         }
+
+        fn partial_compare(&self, other: &dyn ContextElement) -> Option<Ordering> {
+            // TODO: Implement
+            None
+        }
     }
 
     #[test]