Testing failures

Sometimes, we want to test that a function will panic. To do so, we can simply add the #[should_panic] attribute at the top of the test function:

    #[should_panic]
    #[test]
    fn test_dummy() {
        assert!(false, "Always fail");
    }

When doing so, the test now passes:

    Finished dev [unoptimized + debuginfo] target(s) in 1.30 secs
     Running target/debug/deps/ftp_server-452667ddc2d724e8

running 2 tests
test codec::tests::test_dummy ... ok
test codec::tests::test_encoder ... ok

test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out