cheat sheets.

Authorize.net Test Credit Cards

370000000000002  - American Express Test Card
6011000000000012 - Discover Test Card
5424000000000015 - MasterCard Test Card
4007000000027    - Visa Test Card
4012888818888    - Visa Test Card II
3088000000000017 - JCB Test Card (Use expiration date 0905)
38000000000006   - Diners Club/Carte Blanche Test (Use expiration date 0905) 

Use any non-expired date for cards without specific expiration dates.