Macro claim::assert_err

macro_rules! assert_err {
    ($cond:expr) => { ... };
    ($cond:expr,) => { ... };
    ($cond:expr, $($arg:tt)+) => { ... };
}

Asserts that expression returns Err(E) variant.

Examples

let res: Result<i32, ()> = Err(());

assert_err!(res);

let res: Result<i32, ()> = Ok(42);

assert_err!(res);  // Will panic