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: main.rs
    path of file: ./repos/aws-sdk-rust/examples/examples/testing/src
    
    the code of the file until where you have to start completion: // Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

use aws_config::meta::region::RegionProviderChain;
// snippet-start:[testing.rust.intro-import]
// So we can refer to the S3 package as s3 for the rest of the example.
use aws_sdk_s3 as s3;
// snippet-end:[testing.rust.intro-import]
use clap::Parser;

// The testing approaches imported as
    
async fn main() -> Result<(), s3::Error> {
    tracing_subscriber::fmt::init();

    let Opt {
        bucket,
        prefix,
        region,
        verbose,
    } = Opt::parse();

    let region_provider = RegionProviderChain::first_try(region.map(s3::config::Region::new))
        .or_default_provider()
        .or_else(s3::config::Region::new("us-west-2"));

    println!();

    if verbose {
        println!("S3 client version: {}", s3::meta::PKG_VERSION);
        println!(
            "Region:            {}",
            region_provider.region().await.unwrap().as_ref()
        );
        println!("Bucket:            {}", &bucket);
        println!("Prefix:            {}", &prefix);
        println!();
    }

    let shared_config = aws_config::from_env().region(region_provider).load().await;
    let client = s3::Client::new(&shared_config);

    let total_size = determine_prefix_file_size(client, &bucket, &prefix).await?;
    println!("Total size: {}", total_size);

    Ok(())
}