Testing Specials

Getting started

Rather than modifying the existing property, which does a fine job of checking non-special prices, we’ll add a new one to check specials. The separation will help narrow down problems when they happen. If the property for basic prices always works, then we’ll know that failures in the separate special property likely relate to bugs in the special one’s handling.

Let’s take a look at the property that we could implement.

property "sums including specials" do
  forall {items, expected_price, prices, specials}
          <- item_price_special() do
    expected_price == Checkout.total(items, prices, specials)
  end
end

This property is similar to the one we wrote earlier, except that we now expect another term ...