Calculating financial transaction sum and tax (VAT)

This started as a project for learning Unit Tests, then to learn the Strategy Pattern, and finely learning some git/github source control.

The code functionality is very simple

Input:

• Enumerable transaction lines , which contains: Id, Tax rate, Tax code, Quantity, and line total.
• Global discounts (amount or percentage, not both)

Output:

An object containing

• Transaction Totals (with and without tax)
• Transaction tax (VAT) split into groups and rates
• All totals are with and without the global discount.

Supports:

• Multiple tax groups and rates
• Add or extract tax method
• Global discount percent or global discount amount
• Positive and negative quantity of items in the same transaction