Does anyone have any methods to perform a test transaction on their live production sites, without it charging the user or sending the order to the warehouse?
Other platforms seem to have a method to do this.
Yes, this is directly from the Magento Community Edition User Guide:
Testing Credentials
When testing the configuration of a payment gateway, use the following credentials for test transactions.
Visa: 4111111111111111
MasterCard: 5555555555554444
American Express: 378282246310005
Expiration Date: Any future date
CVV/CVC: 123 or 000
You can use test card numbers in your live site. However it will send the order data to Magento.
I believe you can cancel the order in admin area once you submit the order.
Magento application test card numbers, For CVC and CVV please use any 3-digit combination for Visa, Mastercard, Discover, Diners Club, EnRoute, and JCB; use a 4-digit combination for American Express.