Once you set up a new vendor and map your products, it's time to send a test order to make sure everything is working as intended before you go Live.
You can send a test order by placing an order in your shopping cart, make sure the order is of a product that is mapped to the proper vendor. Alternatively, you can look for an older order (could be a live order) and reprocess it in Spark Shipping.
It is important to let the vendor know you're sending a test order, to get their feedback and to make sure the order doesn't get fulfilled.