They were probably one of the most closely guarded pieces of equipment we had since the cards that cleared did so at any merchant so it'd work at point of sale but the vendor would never receive the money.

They're fairly large processing over $40b in annual transaction volumes, and there wasn't any stress about not doing it again post testing (the only stress was the customer wanting a refund for the transaction costs).

If it is a merchant bank, or network requirement, it's either explicitly for card not present transactions, or not well followed. The important factor was handling of the credit card information (PCI DSS compliance).

Noob question: Would using a debit card test the payment system without the self loan float?