CVV Test Framework: Sandbox Tests for Card Codes

Answer

A CVV test framework is a set of sandbox card numbers, format rules, and assertions that check how a payment integration handles the card security code. It does not test a real card. The test values come from a payment processor and work only against sandbox endpoints.

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What the code is

Visa, Mastercard, and Discover print a 3-digit value on the back of the card. American Express prints a 4-digit code on the front. The issuer generates the code. It is not derived from the card number, and it has no checksum. A Luhn check validates the primary account number, not the CVV.

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What the framework covers

• Format validation: digits only, fixed length, no spaces.
• Brand rules: 3 digits for Visa, Mastercard, and Discover; 4 digits for American Express.
• PAN checks: Luhn, length, and BIN range.
• Expiry checks: month 01 to 12, and a card that is not expired.
• Sandbox responses: approvals, declines, and error codes tied to specific test numbers.
• Negative cases: empty field, 2 digits, 5 digits, letters, and pasted whitespace.

Where the test values come from

Stripe, Adyen, Braintree, and other processors publish test card numbers. Those numbers pass Luhn and the format rules, and they route to sandbox endpoints. Any future expiry date works. The CVV field accepts any 3 digits, or 4 digits for Amex test numbers, unless the processor documents a fixed value.

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Assertions to write

1. The form rejects non-digit input in the code field.
2. The form rejects a 3-digit code on an Amex test card.
3. The code never appears in application logs, error traces, or analytics events.
4. The code is not written to the database after authorization.
5. The request to the processor uses TLS, and the code goes to the processor only.
6. A decline response shows a generic message with no field detail.

What the framework must not do

Never run tests against live card numbers. PCI DSS classifies the CVV as sensitive authentication data and prohibits storing it after authorization. A test environment that holds real cardholder data falls in scope for PCI DSS. Use published test values and nothing else.

Limits

A test framework confirms format handling and integration behavior. It cannot confirm how an issuer validates a real code, because that check happens only on a live authorization. Sandbox approvals are simulated. Treat the framework as a check on code paths, not on fraud controls.