We made testing your workshop addons as easy as possible. To get started, hop into the editor from the main menu.
Once you're in the editor you'll see a side bar that has My Uploads and My Imports.
My Uploads - Displays a list of items that you have uploaded.
My Imports - Displays a list of items that you have imported.
To test/preview your uploaded content simply click on the button. It'll download the addon straight from Steam and display it as it is show in-game for everyone.