Update datafusion/src/logical_plan/expr.rs

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

datafusion/src/logical_plan/expr.rs

@@ -2243,7 +2243,7 @@ mod tests {
                 assert_eq!(name, fun);
                 assert_eq!(expected.len(), args.len());
             } else {
-                assert!(false, "unexpected");
+                assert!(false, "unexpected: {:?}", result);
             }               
         };  
     }