Test 4: Test Credit Card Validity

Input:

A string representing the credit card number and two integers representing the month and year when the card expires.

Tests:

1.  Check that all bytes in the string are digits.

2.  Check that the month lies between 1 and 12 and the year is greater than or equal to the current year.

3.  Using the first 4 digits of the credit card number, check that the card issuer is valid by looking up the card issuer table.  Check credit card validity by submitting the card number and expiration date information to the card issuer.

Output:

OK or error message indicating that the card is invalid