Macro equal 

macro_rules! equal {
    ($a: expr, $b: expr) => { ... };
}

Assert that a equal to b, otherwise it return an error.

For example:

fn expect_equal(a: u64, b:u64) -> Result<(), Box<dyn Error + 'static>> {
    equal!(a,b);
    Ok(())
}
assert!(expect_equal(2,2).is_ok());
assert!(expect_equal(3,2).unwrap_err().to_string().starts_with("expect: a(3) == b(2) at "));