We send WP the same order number for the initial 10 cent test charge as we do for the full donation authorization. Worldpay generates a unique PTTID for each transaction. Currently, WP uses the unique PTTID in its communication with the donor's financial institution. In order to make refunds less of a manual process, WP can switch to using our order number as the transaction identifier between itself and the financial institution. Using each order number twice would be a problem.

https://gerrit.wikimedia.org/r/171561 generates unique order ids by appending a different digit for each transaction in a donation. The sale transaction will keep the standard order ID for ease of correlation on refunds.

TODO: update regex in audit script to find log lines with postfixed digits.

More info from donor services: https://wikimedia.mingle.thoughtworks.com/projects/online_fundraiser/cards/2144