A project to track SKUs in a shopping basket, and to calculate the basket total given a set of pricing rules.

• SKU prices and basket totals can be held in a Long
• Pricing rules can be applied in isolation: i.e. the result of a rule is not affected by the behaviour of another rule
• Each SKU in the basket is priced by one, and only one, pricing rule
• Multi-buy discounts are applied repeatedly for each qualifying group of items

A rule applying to a single SKU. The total is the SKU price multiplied by the number of instances of the SKU in the basket.

A rule applying to a single SKU. When a qualifying number of the SKU are present in the basket, a discounted price is applied. The total is the discounted price for each group of qualifying items, plus the single item price for each remaining item.

New rules can be added by implementing the PricingRule interface. Single SKU rules such as percentage or tiered discounts would be variations on the current rules. Since the appliesTo logic is implemented in the rule, more complex rules that apply to multiple SKUs could be added. For example, discounts for SKUs bought together, that delegate to unit pricing rules if not satisfied. The invariant that one, and only one, pricing rule prices each SKU must hold.

There are unit tests covering the behaviour of the rules and validation. In addition there are some tests covering some selected baskets of the "current" prices.