In developer mode, I've tested credit cards that usually give the correct response (invalid expiration date, invalid card number, accepted, etc.). However, when I enter in my credit card and intentionally put in something incorrect (such as wrong year) and pass it through, it goes through as accepted. This shouldn't happen because it's not an actual valid card, yet I can't seem to get the proper error response to appear, just that it's accepted.
How can I go about getting this to work in development? This applies to any scenario where a card should be declined and the transaction shouldn't return a success, but still does.