Fixed version of Nashenas88's test-case macro

playground.rs

macro_rules! as_item { ($i:item) => ($i) } // <-- empirically, this is needed to placate the compiler
macro_rules! test_cases {
    (
        $test_name:ident
        $param_names:tt, // <-- just treat the param names as a tuple (type 'tt' to delay parsing)
        [$($case_name:ident : $test_params:tt)+] // <-- same for the param values
        $test_code:block
    ) => (as_item!(
        #[cfg(test)]
        pub mod $test_name {
        $(
            #[test]
            #[allow(non_snake_case)]
            fn $case_name () {
                let $param_names = $test_params;
                $test_code
            }
        )+}
    ););
}

test_cases!(
    test_hex_to_base_64
    (hex_str, expected_base64_str),
    [
        A: ("49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d", "SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t")
        B: ("49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6", "SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29g")
        C: ("49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f", "SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb28=")
        D: ("49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6", "SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb2A=")
        E: ("49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f", "SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hybw==")
        F: ("49276d206b696c6c696e6720796f75722x627261696e206c696b65206120706f69736f6e6f7573206d757368726", "49276d206b696c6c696e6720796f75722x627261696e206c696b65206120706f69736f6e6f7573206d757368726")
    ] // NB: I changed test case F so that it will fail
    {
        assert!(hex_str != expected_base64_str);
    }
);