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: stdio.rs
    path of file: ./repos/wasmer/lib/virtual-fs/src/mem_fs
    
    the code of the file until where you have to start completion: //! This module contains the standard I/O streams, i.e. “emulated”
//! `stdin`, `stdout` and `stderr`.

use crate::{FsError, Result, VirtualFile};
use std::io::{self, Write};

macro_rules! impl_virtualfile_on_std_streams {
    ($name:ident { readable: $readable:expr, writable: $writable:expr $(,)* }) => {
        /// A wrapper type around the standard I/O stream of the same
  
    
    async fn test_write_stderr() {
        let mut stderr = Stderr { buf: vec![] };

        assert!(
            matches!(stderr.write(b"baz").await, Ok(3)),
            "writing into `stderr`",
        );
        assert!(
            matches!(stderr.write(b"qux").await, Ok(3)),
            "writing again into `stderr`",
        );
        assert_eq!(
            stderr.buf,
            &[b'b', b'a', b'z', b'q', b'u', b'x'],
            "checking the content of `stderr`",
        );
    }