Write Production Without Test

discountRateByMembershipType.php

<?php
function discountRateByMembershipType($userId) {
    //$date = getCurrentDateFromLocalTimeOrRemoteTimeServer(); //with remote time server, we can't fake date
    //if (is_not_black_friday($date) return 0; // we can't not test CORE BUSINESS if add this spec
    $membershipType = getMemberShipTypeFromDatabaseOrRemoteApi($userId);
    //CORE BUSINESS need coverage by unit test or manual test 
    if ('platinum' === $membershipType) return 0.15;
    if ('gold'     === $membershipType) return 0.1;
    if ('slive'    === $membershipType) return 0.05;
    throw new UnknowMembershipTypeException('invalid membership type');
}