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: async.rs
    path of file: ./repos/flume/tests
    
    the code of the file until where you have to start completion: #[cfg(feature = "async")]
use {
    flume::*,
    futures::{stream::FuturesUnordered, StreamExt, TryFutureExt, Future},
    futures::task::{Context, Waker, Poll},
    async_std::prelude::FutureExt,
    std::{time::Duration, sync::{atomic::{AtomicUsize, Ordering}, Arc}},
};

#[cfg(feature = "async")]
#[test]
fn r#async_recv() {
    let (tx, rx) = unbounded();

    let t = std::thread::spawn(move || {
        std::thread::sleep(std::time::Duration::from_millis(250));
        tx.send(42u32).unwrap();
    });

    async_std::task::block_on(async {
        ass
    
fn spsc_single_threaded_value_ordering() {
    async fn test() {
        let (tx, rx) = flume::bounded(4);
        tokio::select! {
        _ = producer(tx) => {},
        _ = consumer(rx) => {},
    }
    }

    async fn producer(tx: flume::Sender<usize>) {
        for i in 0..100 {
            tx.send_async(i).await.unwrap();
        }
    }

    async fn consumer(rx: flume::Receiver<usize>) {
        let mut expected = 0;
        while let Ok(value) = rx.recv_async().await {
            assert_eq!(value, expected);
            expected += 1;
        }
    }

    let rt = tokio::runtime::Builder::new_current_thread().build().unwrap();
    rt.block_on(test());
}