Kantox Technical Evaluation

Objetives

Evaluation of programming style
Evaluation of language knowledge
Evaluation of testing approach

Technical requirements

Use Ruby language (not Ruby on Rails)
Use TDD (Test-Driven Development) methodology
Use github as public repository
Use of DB is not required

Deadline

Assignment should be ready within 5 natural days of inbox reception
Assignment is completed when we receive the link to the repository

Assignment:

You are the lead programmer for a small chain of supermarkets. You are required to make a simple cashier function that adds products to a cart and displays the total price.

You have the following test products registered:

Product code	Name	Price
GR1	Green tea	£3.11
SR1	Strawberries	£5.00
CF1	Coffee	£11.23

Special conditions

The CEO is a big fan of buy-one-get-one-free offers and of green tea. He wants us to add a rule to do this.
The COO, though, likes low prices and wants people buying strawberries to get a price discount for bulk purchases. If you buy 3 or more strawberries, the price should drop to £4.50
The CTO is a coffee addict. If you buy 3 or more coffees, the price of all coffees should drop to two thirds of the original price.

Our check-out can scan items in any order, and because the CEO and COO change their minds often, it needs to be flexible regarding our pricing rules. The interface to our checkout looks like this (shown in ruby):

co = Checkout.new(pricing_rules)
co.scan(item)
co.scan(item)
price = co.total

Implement a checkout system that fulfills these requirements.

Test data: Basket: GR1,SR1,GR1,GR1,CF1

Total price expected: £22.45

Basket: GR1,GR1

Total price expected: £3.11

Basket: SR1,SR1,GR1,SR1

Total price expected: £16.61

Basket: GR1,CF1,SR1,CF1,CF1

Total price expected: £30.57

Doc after finish the project

Usage

irb

require './lib/item'
require './lib/checkout'

gr1 = Item.new('gr1', 'Green tea', 3.11)
sr1 = Item.new('sr1', 'Strawberries', 5.00)
cf1 = Item.new('cf1', 'Coffee', 11.23)

pricing_rules = []
pricing_rules << BuyXGetYFree.new(gr1, 2, 1)
pricing_rules << DiscountWithMinQuantity.new(sr1, 3, 4.50, false)
pricing_rules << DiscountWithMinQuantity.new(cf1, 3, 2.0/3, true)

co = Checkout.new(pricing_rules)
co.scan(gr1)
co.scan(sr1)
co.total

Decisions

I decided to split the development in four parts, each part is formed by the write of the tests and after that, the write of the code in order to apply TDD to the whole project:

1: Implement the main classes (Checkout, Item, Pricing Rule)
2: Implement the function scan (inside the Checkout class)
3: Implement the function total (without discounts and offers, to make sure that it adds the results properly)
4: Finish the function total behaviour adding the offers, I had only to add code to the subclasses of PricingRule

Extra step: Make a whole check in order to be sure that it works great. In this step I saw that I had to modify the requires (to relative_requires) and I can use a super function inside the apply method inside DiscountWithMinQuantity class.

Additional comments

I used CircleCI in order to test the suite correctly, I can saw it in the interview if you want.
Wrote in MacOS using RVM.

Possible improvements if I had more time:

Add a mock for a database (or real database)
Add methods and classes to print the currency and make a converter (if there are more than one currency in the same store, maybe an online store?)

JMavs/kantox