Bundle Configurator

• Pair-Programming
• Outside-in TDD
• Difficulty: Competent
• Estimated Duration: 1 hour 30 minutes

Problem

A customer can add single products to their cart. Once the customer is done selecting single products, they go to the checkout and there will be display the cheapest combination of bundles and single product as possible.

Bundle products are a combination of single products which are usually cheaper than buying them separately. The goal is to build a function that given a list of single products it will return the best (cheapest) solution, taking in consideration the prices for single and bundle products.

Requirements

A Customer can select only single products, so the algorithm should check if there is a bundle that matches those products, and in that case provide the cheapest option in comparison with the single product prices totals.

Product, Bundles and Prices

A customer can select single products (P = Product):

product	single price
P1	10 EUR
P2	20 EUR
P3	30 EUR
P4	40 EUR
P5	50 EUR

And internally, the system has better prices when buying these products in combinations. These are known as bundle products (B = Bundle):

bundle	products	bundle price	original price
B1	P1,P2	25 EUR	30 EUR
B2	P1,P4	40 EUR	50 EUR
B3	P3,P4	60 EUR	70 EUR
B4	P1,P2,P3,P4	80 EUR	100 EUR
B5	P1,P5	50 EUR	60 EUR

Acceptance Criteria

Given I am a customer
When I add to my cart these products <select>
And I go to the checkout page
Then I will see the <result> products

The order is irrelevant (P1,P2 === P2,P1)

select	result
P1	P1
P1,P2	B1
P2,P1	B1
P1,P2,P3	B1,P3
P1,P3,P4	P1,B3
P1,P2,P3,P4	B4
P2,P4	P2,P4
P2,P3,P4	P2,B3
P3,P4	B3

Extra: the cheapest win

Keep the cheapest when there are multiple possible solutions:

select	result
P1,P2,P5	B5,P2

For example: P1,P2,P5 could result into B1,P5(price: 25 + 50 = 75) or B5,P2 (price: 50 + 20 = 70); therefore B5,P2 is the cheapest and the desired solution.

Tech hint

• Start writing a test that cover one happy path from the requirements.
• It's up to you to define the internal data structure that you want to work on.
• It should be possible to modify the products and bundles without altering the final logic.

Original idea

• https://github.com/teufelaudio/web-it_katas/tree/master/tdd/bundle-configurator