use anyhow::anyhow;
use std::error::Error as StdError;
use std::fmt::{self, Display};
use std::io;
#[derive(Debug)]
enum TestError {
    Io(io::Error),
}
impl Display for TestError {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        match self {
            TestError::Io(e) => Display::fmt(e, formatter),
        }
    }
}
impl StdError for TestError {
    fn source(&self) -> Option<&(dyn StdError + 'static)> {
        match self {
            TestError::Io(io) => Some(io),
        }
    }
}
#[test]
fn test_literal_source() {
    let error = anyhow!("oh no!");
    assert!(error.source().is_none());
}
#[test]
fn test_variable_source() {
    let msg = "oh no!";
    let error = anyhow!(msg);
    assert!(error.source().is_none());
}
#[test]
fn test_fmt_source() {
    let error = anyhow!("{} {}!", "oh", "no");
    assert!(error.source().is_none());
}
#[test]
fn test_io_source() {
    let io = io::Error::new(io::ErrorKind::Other, "oh no!");
    let error = anyhow!(TestError::Io(io));
    assert_eq!("oh no!", error.source().unwrap().to_string());
}