#[derive(Debug)]
struct TestError {
    test: String,
}

impl std::fmt::Display for TestError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(
            f,
            "TestError::Display test: {}",
            self.test,
        )
    }
}

impl std::error::Error for TestError {
    fn description(&self) -> &str {
        "TestError::description"
    }
}

fn return_error() -> Result<(), TestError> {
    Err(TestError{ test: "return_error".to_string() })
}

fn main() {
    println!("{}", return_error().err().unwrap());
    println!("{:?}", return_error().err().unwrap());
    return_error().expect("expect in main");
}