Test purchases can be made in your shopping cart by setting up a "comp" (complimentary) payment option temporarily.
Add a New Paymentt Method
A new payment method can be added from the right side of the control panel under Payment Settings Payment Methods
Add a New Method
Click on the button
Payment Method Code
Payment Method Description
Payment Method Status
Select 'active' from the drop down menu.
Click the button
Test the Shopping Cart Purchase
Under the Payment Method section of the checkout form, choose 'comp' from the drop down menu.
IMPORTANT - Deactivate the Comp Payment Method
When testing has been completed, edit the comp payment method and set the status to 'inactive'. Otherwise, anyone making a purchase could choose this method.