You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: visit.rs
    path of file: ./repos/materialize/src/expr/src
    
    the code of the file until where you have to start completion: // Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this software is governed by the Business Source License
// included in the LICENSE file.
//
// As of the Change Date specified in that file, in accordance with
// th
    
    fn test_recursive_types_a() {
        let mut act = test_term_rec_a(0);
        let exp = test_term_rec_a(20);

        let res = act.visit_mut_pre(&mut |expr| match expr {
            A::Lit(x) => *x = *x + 20,
            _ => (),
        });

        assert!(res.is_ok());
        assert_eq!(act, exp);
    }