Function err_into 

pub fn err_into<T, E>(a: Result<T, E>) -> E
where
    T: Debug,
    E: Debug,

Asserts that the value is err and returns the value.

Example

use common_testing::assert;

#[test]
fn test_1() {
 let result = Err("abc");
 let err = assert::err_into(a);
 assert::equal(err, "abc");
}