How to test for Super Admin

I got it to work as follows — in mu-plugins directory, my superAdmin.php script looks like this:

<?php

function check_for_superAdmin($user_login, $user) {
    $current_user = get_userdatabylogin($user_login);
    if ( is_super_admin( $current_user->ID ) ) { // do these things }
    else { // do other things }
}
add_action( 'wp_login', 'check_for_superAdmin', 10, 2 );

?>

Hope this helps someone wanting to hook the same way.