    assert!(readable.skip_bytes(1).is_ok());
    assert_eq!(readable.read_string(1).unwrap(), "B");
    // utf8, 3bytes
    assert_eq!(readable.read_string(3).unwrap(), "가");
    assert_eq!(readable.read_string(5).unwrap(), "나01");
    assert!(readable.read_bytes(1).is_err());
}

#[test]
fn readable_file() {
    let mut readable = File::open("./test-resources/file1.txt").unwrap();
    assert!(readable.read_bytes(10).is_ok());
    assert!(readable.read_bytes(10).is_ok());