Go to the public site, add something to your cart, and go to Checkout.
When you get to the checkout page, try all of your payment methods.
Credit Card
Put in a fake card number like 4100000000000000. When you try to checkout, the system should come back with an "invalid credit card number" error (or something like that).
PayPal
Just click the "Submit Your Order" and you should be taken to a PayPal login page that shows your company at the top of the page.
(NOTE: the order will show up under Orders > Incomplete (tab). You can delete it.
Check / Money Order / Phone In
These orders should go straight through and be found in Orders > Incomplete (tab).