Macro assertables::assert_fn_err_lt_as_result

macro_rules! assert_fn_err_lt_as_result {
    ($function:path, $a_input:expr, $b_expr:expr $(,)?) => { ... };
}

Assert one function ok() is less than another.

• When true, return Result Ok(()).

• When true, return Result Err with a diagnostic message.

Examples

fn example_digit_to_string(i: i32) -> Result<String, String> {
    match i {
        0..=9 => Ok(format!("{}", i)),
        _ => Err(format!("{:?} is out of range", i)),
    }
}

let a = 10;
let b = String::from("20 is out of range");
let x = assert_fn_err_lt_as_result!(example_digit_to_string, a, b);
//-> Ok(())
let actual = x.unwrap();
let expect = ();
assert_eq!(actual, expect);

let a = 20;
let b = String::from("10 is out of range");
let x = assert_fn_err_lt_as_result!(example_digit_to_string, a, b);
//-> Err(…)
let actual = x.unwrap_err();
let expect = concat!(
    "assertion failed: `assert_fn_err_lt!(function, left_input, right_expr)`\n",
    "    function name: `example_digit_to_string`,\n",
    "  left input name: `a`,\n",
    "  right expr name: `b`,\n",
    "       left input: `20`,\n",
    "       right expr: `\"10 is out of range\"`,\n",
    "      left output: `\"20 is out of range\"`,\n",
    "             left: `\"20 is out of range\"`,\n",
    "            right: `\"10 is out of range\"`"
);
assert_eq!(actual, expect);