Tips and Tricks for testing credit cards validation

1. The following test credit cards validate properly but are not actually in use (http://support.microsoft.com/kb/258255):

AMERICAN EXPRESS: 3111-1111-1111-1117
VISA - 4111-1111-1111-1111
MASTERCARD - 5111-1111-1111-1118
DISCOVER - 6111-1111-1111-1116

2. How to test over limit on a credit card?

Use a prepaid VISA gift card. Pick one for 25$, go over the limit, see what happens when the card is declined. This is great as there is no revealing of personal card information in the wild

Source: http://www.testthisblog.com