Actualy question says all, I need this only for testing. So, demo of some kind or 4-5 free transactions a day will do a trick.
Not looking for anything fancy.
Is there anything free?
Use a paypal developer account. They have a sandbox that is identical to the real thing except it doesn't process transactions.
If you use the back end webservice functions (not the forms based api) it should do what you want.
I dont' think it will do AVS for you though.