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: test_runner.rs
    path of file: ./repos/materialize/src/expr-test-util/tests
    
    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
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0.

mod test {
    use mz_expr_test_util::*;
    use mz_lowertest::{serialize, MzReflect, TestDeserializeContext};
    use mz_ore::result::ResultExt;
    use serde::de::DeserializeOwned;
    use serde::Serialize;

    /// Build a object of type `T` from the test spec, turn it back into a
    /// test spec, construct an object from the new test spec, an
    
    fn roundtrip_with_catalog(orig_spec: &str, orig_catalog: &TestCatalog) -> Result<(), String> {
        let orig_rel = build_rel(orig_spec, orig_catalog)?;
        let json = serde_json::to_value(orig_rel.clone()).map_err_to_string_with_causes()?;
        let mut new_catalog = TestCatalog::default();
        let (new_spec, source_defs) = json_to_spec(&json.to_string(), &new_catalog);
        for source_def in source_defs {
            new_catalog.handle_test_command(&source_def)?;
        }
        let new_rel = build_rel(&new_spec, &new_catalog)?;
        if new_rel.eq(&orig_rel) {
            Ok(())
        } else {
            Err(format!(
                "Round trip failed. New spec:\n{}
            Original relation:\n{}
            New relation:\n{}
            JSON for original relation:\n{}",
                new_spec,
                serde_json::to_string_pretty(&orig_rel).unwrap(),
                serde_json::to_string_pretty(&new_rel).unwrap(),
                json,
            ))
        }
    }