When you are ready to begin testing your Apps Merchant account you should use a fake (but valid) credit card number.
Fill in your complete information, and make certain that the Expiration Date is later then the current one!
Here’s the list of test card numbers to use:
– American Express Test Card: 370000000000002
– Discover Test Card: 6011000000000012
– Visa Test Card: 4007000000027
– Second Visa Test Card: 4012888818888
– JCB: 3088000000000017
– Diners Club/ Carte Blanche: 38000000000006
– Second MasterCard Test Card: 5105105105105100