Run rake run
ruby2d gem need some specifics stuff. For linux:
sudo apt install libsdl2-dev libsdl2-image-dev libsdl2-mixer-dev libsdl2-ttf-dev
You can find more information here: https://www.ruby2d.com/learn/linux/#install-packages
Run bundle install
Run rake app:spec
To get covering repport run rake app:spec:coverage
Run rake app:linter:all