This Checkout challenge has been created with SOLID principles and BDD approach. New promotional rules can be added without changing the implemantation (open for extension, closed for modification). The given implementation requirements have been translated into acceptance specs in order to follow a BDD approach.
How to use:
bundle install
# Unit tests
rspec
# Features tests
rspec spec/features/*The feature tests also provide a way to see how to setup and use the checkout system.