Short answer
A card validation test checks the format of a card number. It does not check if the card exists, if it has funds, or if the person typing it holds the card. Three rules cover most tests: the Luhn checksum, the digit count for the brand, and the issuer range in the first digits.
What "v8" refers to
No payment brand publishes a document called card validation test v8. Visa, Mastercard, and ISO publish no version 8 of a card number test. A tool with that label is a private build. Read the label as a product name, not a standard.
Card Validation Test v9: What It Checks and How to Run It
The Luhn check
Luhn mod-10 is the checksum on most card numbers. Start at the rightmost digit and double every second digit. Subtract 9 from any result above 9. Add all digits. A total that divides by 10 passes.
Card Validation Test v7: What It Covers and How to Run It
Luhn is weak on its own. About 1 in 10 random digit strings passes. A pass means the digits are well formed. Nothing more.
Length and issuer range
Each brand sets a digit count. Visa uses 13, 16, or 19 digits. Mastercard uses 16. American Express uses 15. The first 6 to 8 digits are the issuer identification number under ISO/IEC 7812. That prefix maps a number to a bank and a country. It does not map a number to an account holder.
Test numbers
Payment processors publish test card numbers for developers. Examples include 4111111111111111 and 5555555555554444. These pass Luhn and route to sandbox systems. Live networks reject them.
Use test numbers on your own systems. Do not send real card data to a test environment.
What a test cannot show
- Authorization result
- Available balance
- Card status, such as lost or blocked
- Owner identity
- 3-D Secure enrollment
Those checks need a request to the issuer through an acquirer. A local check cannot produce them.
Storage and scope
PCI DSS applies to any system that stores, processes, or transmits cardholder data, including test rigs that hold real numbers. Keep test data synthetic. Log the result of a check, not the number.