The extensions folder contains a little bit of code thats loaded as a hardhat plugin into the console. Essentially, the variable game is an instance of the Game class which you see in extensions/play.js - yes the name of the file doesn't match, I know.
Anyhow, if you look at the Game class, and the Adventurer class, you'll see how it sets up a basic 'harness' or tool for playing the game from inside the console. It needs work but its a start.
The other thing which makes this work is the change to deploy.js - at the end of the script, it shits out all the addresses of the contracts to addresses.json in the root of the project. This is loaded by our Game plugin so that you don't have to map addresses manually.
npx hardhat coverage