Install ruby, bundler and rubygems. Follow this tut;
Run # bundle
command to install all needed ruby dependencies
Inside <app root path>
run:
$ ruby calculate.rb '1, imported bottle of perfume, 32.19 1,bottle of perfume, 20.89 1,packet of headache pills, 9.75 1, imported box of chocolates, 11.85'
Inside <app root path>
run $ rspec spec/modules/*
.
All spec files can be found under <app root path>/spec
directory;
Inside <app root path>
run $ rubocop
.