When you cancel an order in ShipStation, it gets automatically moved into the "Cancelled" view in the Orders tab. Please note that whenever you cancel an order in ShipStation, that order status change will not be reflected in your shopping cart or marketplace. This is because we want your shopping cart/marketplace to be the place of record for your orders. Thus, when you cancel an order in your shopping cart/marketplace, the order status will update as such in ShipStation.
To cancel an order in ShipStation, simply find the order on the Orders screen, select it, and click the Cancel Order button. Click Yes, Please Proceed... to confirm your choice, and then that order will only show up in the "Cancelled" view of the Orders tab.
If you have the express intent of doing test orders, creating a manual store (by which you can create orders that have no direct correlation to any of your connected stores) may be your best option. In this way, you can create as many manual orders as you need, either one-by-one or through CSV import. Then, when you're done testing, you can make that store inactive to hide the orders (and store) completely.