When testing Authorize.Net (AIM) I notice the following:
If you chose pick-up and select Authorize.Net (AIM) as payment you receive this alert: (TESTMODE) Bill To Address is required. The problem is you can't enter an address. If you select Authorize.Net (AIM) as payment you should be requested for a billing address and also a delivery address if different from the billing address.
( although you receive the error message the sale still shows in admin under orders )
Also in test mode there are various post codes and instructions you can enter to trigger a failed transaction, such as the one below below. I have tested this and others and all sales go through instead of triggering the failed transaction. ( these details are from the developer page of Authorize.net. )
Zip Code: 46282 should trigger the following: This Transaction has been declined.
I did test this earlier before testing the developer and it did work.
In addition to the above I ran a test where I didn't enter any details for the credit card and the checkout page just refreshed with no error message. But the sale still showed in admin under orders.