First you'll need to go here and download and fund a demo wallet.
Then you can use this test harness.
If you select CartSummary then either SubTotal or Total is a required input.
If you select CartDetails then either SubTotal or Total is a required input *or* you need to supply at least the description and unit price for the first item. (The CPG supports more than 2 items - I just made the test form with two.)
Basically if there is a total, that's what is charged - done. If there is a subtotal then it is added up with taxes, shipping, handling, and discount - done. If both are missing and it is in details then all the item calculations are done. If both are missing and it is summary - you get an error notice.
Whatever email you enter for the merchant email will get the merchant emails - same for customer email. Note, the look and feel of the emails and HTML pages WILL CHANGE. I'm still trying to get all that XSL overhauled, but the past week has SUCKED and I've been totally sacked on debugging server problems, etc, and haven't had the cycles. So I know the look and feel is kind of weak - like right now the consumer and merchant get the same email, etc.
If something blows up or you think it is being wonky, please let me know what you did so I can recreate it.
If there are any questions about what the fields do, etc, post here so everyone can see.
Feedback is most welcome. Please send it to me at work - megazone at cyphermint dot com.