My implementation of the volume pricing exercise.
All code is in main.rb
All specs are in spec_volume_pricing.rb
An example matching the one given is in example.rb
Code assumes that if there is a price $X/unit when you buy 1, and $Y/unit when you buy 4, that the cost of 5 is 4Y + X, as opposed to 5Y. This is how the given examples work.
Test cases are not comprehensive.