You guys really should check your plugin out with debug mode turned on, lots of php warnings and notices.
Also, after doing a bit of research on how to delete test orders, it seems that officially, the only way is to go in and manually remove orders from the database using phpMyAdmin, etc.
However, 7 months ago, Aaron did mention that he's added this to my todo list for features.
That being said, we went ahead and fixed many of the php issues (mostly verifying that variables exist before checking their values) and added the ability to delete orders. Not just from the wp_post table, but also all related wp_post_meta entries for the order. Even though Aaron worries that deleting orders may
seem way too dangerous to include in the admin areawe feel it's kind of a basic feature and quite safe for adults who employ reason and cognitive thinking skills.