How to Test Payment Gateway
Functionality?

To test
payment gateway functionality is same as test any other functionality. You
should have some test strategy during testing it. Following are some points
keep in mind during testing of payment gateway.

1. Gather appropriate test data
   for the dummy credit card numbers for various master cards.
2. Gather payment gateway
   information like whether used paypal, guestpay etc.
3. Gather payment gateway
   documents with error codes – useful it if any error came during testing to
   identify whether its our application fault or payment gateway related
   error.
4. Does the gateway do what it
   is supposed to do? Does it handle order objects correctly? Does it perform
   additional calculations correctly?
5. Understanding of the integration
   of the payment gateway with application
6. Understand and test the
   parameters and sessions passed through payment gateway and application
7. Understand and test the
   amount related information passed through query string or session or
   variables in any form.
8. Check the format of the
   amount with currency format
9. Check the language of the
   application and payment gateway language
10. Try to change payment gateway
    language during the payment process
11. Test after successful payment
    all the necessary data retrieved to our application or not
12. Check what happens if payment
    gateway goes down during the payment process
13. Check what happens if payment
    process went successful but do not return to our application
14. Check what happens if session
    goes time out during the payment process
15. Check what happens in backend
    during the payment process is the session data stored in temporary table
    or any id is generated or not?
16. Check what happens if payment
    process is fail
17. Check if any modification
    transaction is going on through payment gateway, then how much amount is
    taken out as modified amount whether required to pay more or not. For
    example- if modified amount is greater than paid amount then and then only
    application redirect to payment gateway otherwise it should not.
18. Verify DB entries for the
    transaction whether they store credit card details and all or not
19. Verify DB entries for the
    amount related fields in database for the fresh transaction, modified
    transaction and canceled transaction.
20. Verify error page during
    payment gateway process
21. Verify security passes for
    the transaction
22. Sometimes payment gateway
    sent confirmation through popup dialogs – so test popup blocker related
    settings also. What happens is popup blocker is on and all this.
23. Check buffer pages between
    application and payment gateway (firefox firebug add-on will be helpful to
    test)

Hope guys, it will be helpful to you in your testing. If
any new points are there then update it in comments, so I also get update in my
knowledge.