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: configuration_change.rs
    path of file: ./repos/exonum/services/supervisor/examples
    
    the code of the file until where you have to start completion: // Copyright 2020 The Exonum Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under 
    
fn main() {
    // Create testkit instance with our test service and supervisor.
    let service = Spec::new(ConfigChangeService).with_instance(SERVICE_ID, SERVICE_NAME, ());
    let mut testkit = TestKitBuilder::validator()
        .with_logger()
        .with_validators(4)
        .with(Supervisor::decentralized())
        .with(service)
        .build();

    // Firstly, lets change consensus configuration and increase `min_propose_timeout`.
    let cfg_change_height = Height(5);

    // Get current configuration and update `min_propose_timeout`.
    let mut cfg = testkit.consensus_config();
    cfg.min_propose_timeout += 1;

    // Create consensus config propose.
    let propose = ConfigPropose::new(0, cfg_change_height).consensus_config(cfg.clone());

    // Sign propose and send it to validators, then wait for its confirmation.
    send_and_vote_for_propose(&mut testkit, propose, cfg_change_height);

    // Check that the proposal has become actual.
    assert_eq!(testkit.consensus_config(), cfg);

    // Secondly, lets change our service configuration. Since config represents as string, lets
    // provide new string value.
    let params = "new value".to_owned();

    let cfg_change_height = Height(10);
    let propose = ConfigPropose::new(1, cfg_change_height).service_config(256, params.clone());

    send_and_vote_for_propose(&mut testkit, propose, cfg_change_height);

    // Check that parameter has been changed.
    let snapshot = testkit.snapshot();
    let actual_params = snapshot
        .for_service(SERVICE_NAME)
        .unwrap()
        .get_entry::<_, String>("params");

    assert_eq!(actual_params.get().unwrap(), params);
}