The registration command is now available for the API. A successful command will create a registration order. You must have enough account balance to pay for the order.
I used the response examples provided by Dynadot and saved them in text files. Then instead of querying Dynadot for response I fetch the file contents (using get_file_contents in php).
So you just edit the file to match the kind of response you want to simulate. As for live tests you can always delete the names as long as they are within the grace peiod.