Hi there. There isn't an option to test codes without them being redeemed. Despite already having the emblem, unfortunately if it said the redemption was successful, then the code was applied to your profile and can't be used again by any other player. Bungie does not issue replacement codes for emblems that have already been redeemed. If you want another, you'd need to contact the company responsible for the giveaway to ask if they can give you another.