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RED SAGSkills
mediumQA Engineer interview question

How would you test a card payment checkout for an e-commerce site in the UAE?

What the interviewer wants to hear

  • Happy paths with gateway test cards, including 3-D Secure
  • Declines, insufficient funds, expired cards, timeouts and gateway errors
  • Double submit, retries, back button and refresh: no double charge, idempotency
  • Amounts, VAT, currency, rounding and refunds; order and payment status stay consistent
  • Security and compliance: no card data in logs, HTTPS, PCI scope
  • Webhooks, reconciliation and notifications such as email or SMS receipts

Model answer

I would use the gateway's sandbox and its test cards. Happy paths cover Visa and Mastercard, saved cards and 3-D Secure challenges. Negative paths cover declined, insufficient funds, expired cards, a failed 3-D Secure step and gateway timeouts, checking that clear messages appear and the order is not marked paid. Next I test the risky edge cases: double-clicking Pay, refreshing during redirect, pressing back and slow networks, making sure the customer is charged only once. I check totals, 5% VAT, discounts, rounding to fils and refunds, both partial and full. I also verify webhooks, since the gateway may confirm a payment after the browser closes, and that order status, payment records and receipts all agree. Finally I confirm card numbers never appear in logs or our database and that everything runs over HTTPS.

Can you answer it under time pressure?

Take a timed medium round and get scored on every answer.

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