Write a program that implements a checkout system of a store. This program takes a set of products as string (ABBDBBAC) representing the products on a basket and returns the total amount to pay. Each product has a fixed price, but some have special discounts.

Table of prices:

Item	Price	Discount
================================  
A		50		3 for 130
B		30		2 for 45
C		20
D		15

Example results:

AA >> 100
AABCDADDCD >> 260
AAABBBCCCDDD >> 310

To run the tests, execute:
npm i to install the dependencies and then
npm run test to run the tests