To effectively test payment gateway functionality, testers should: 1. Gather test data like dummy credit card numbers and payment gateway information. 2. Verify the gateway handles orders and payments correctly by testing parameters, sessions, amounts, currencies, and languages passed between the gateway and application. 3. Simulate errors and exceptions like timeouts, failed payments or sessions, and downed gateways to ensure proper behavior.

1. 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.