Clearer error in tests

Author: toml01

src/contract.rs

@@ -1129,7 +1129,9 @@ mod tests {
     fn extract_error_msg<T: Any>(error: StdResult<T>) -> String {
         match error {
             Ok(response) => {
-                let bin_err = (&response as &dyn Any).downcast_ref::<Binary>().unwrap();
+                let bin_err = (&response as &dyn Any)
+                    .downcast_ref::<Binary>()
+                    .expect("An error was expected, but no error could be extracted");
                 match from_binary(bin_err).unwrap() {
                     QueryAnswer::ViewingKeyError { msg } => msg,
                     _ => panic!("Unexpected query answer"),