Crate dyn_error

This crate provides error-related utilities.

In particular, the assert_err_box macro is a minimalist way to test the inner value of an Err<Box<dyn Error>> from a Result:

use dyn_error::*;
use std::fmt::Display;
use std::error::Error;

#[derive(Debug, PartialEq, Eq)]
struct MyErr(pub u8);

impl Display for MyErr {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "Custom error: {}", self.0)
    }
}

impl Error for MyErr {}

let result: Result<String, Box<dyn Error>> = Err(Box::new(MyErr(90)));

assert_err_box!(result, MyErr(90));

For more fine-grained control, the check_err_box function performs the same test but returns a Result in lieu of calling panic:

use dyn_error::*;
use std::fmt::Display;
use std::error::Error;

//
// Declaring a custom Error type
//
#[derive(Debug, PartialEq, Eq)]
struct MyErr(pub u8);

impl Display for MyErr {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "Custom error: {}", self.0)
    }
}

impl Error for MyErr {}

//
// Test scenarios
//
let result: Result<String, Box<dyn Error>> = Err(Box::new(MyErr(90)));
assert_eq!(
    check_err_box(result, MyErr(90)),
    Ok(())
);

let result: Result<String, Box<dyn Error>> = Err(Box::new(MyErr(90)));
assert_eq!(
    check_err_box(result, MyErr(7)),
    Err(ErrBoxCheckFailure::NotEqual {
        expected: "Custom error: 7".to_string(),
        actual: "Custom error: 90".to_string()
    })
);

Macros

• assert_err_box
  Macro that internally calls check_err_box, issuing panic in case of failure.

Enums

• ErrBoxCheckFailure
  Unsuccessful outcome of check_err_box.

Functions

• check_err_box
  Tests whether the given Result is actually an Err with a Box containing an Error implementation equal to the expected instance: