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: send.rs
    path of file: ./repos/sozu/lib/src/protocol/proxy_protocol
    
    the code of the file until where you have to start completion: use std::{
    cell::RefCell,
    io::{ErrorKind, Write},
    rc::Rc,
};

use mio::{net::TcpStream, Token};
use rusty_ulid::Ulid;

use crate::{
    pool::Checkout,
    protocol::{
        pipe::{Pipe, WebSocketContext},
        proxy_protocol::header::{Command, HeaderV2, ProxyProtocolHeader},
    },
    socket::SocketHandler,
    sozu_comma
    
    fn it_should_send_a_proxy_protocol_header_to_the_upstream_backend() {
        setup_test_logger!();
        let addr_client: SocketAddr = "127.0.0.1:6666".parse().expect("parse address error");
        let addr_backend: SocketAddr = "127.0.0.1:2001".parse().expect("parse address error");
        let barrier = Arc::new(Barrier::new(3));
        let end_barrier = Arc::new(Barrier::new(2));

        start_client(addr_client, barrier.clone(), end_barrier.clone());
        let backend = start_backend(addr_backend, barrier.clone(), end_barrier);
        start_middleware(addr_client, addr_backend, barrier);

        backend
            .join()
            .expect("Couldn't join on the associated backend");
    }