If you're lazy like me...
Create a new Google Apps Script on your drive.
Paste Code.gs into Code.gs.
Create a new Test Deployment of type Editor Add-On.
Create a new Test.
Select a designated gdoc where you want it loaded as the "Test file".
There!
An alternative is to create a document, open its GAS editor, paste the addon there, and use this as a prototype (I guess it works like VBA in that regard). You should probably use this method for a one-off, it skips the whole DANGER AUTHORIZING UNKNOWN APP GO BACK GO BACK. These VBA style deployments are scareware free.
The proper alternative is to figure out the 47 steps Google want you to take to publish this legitimately. Bleh, I say!