public void Two_A_should_be_100()
 {
     var checkout = new Checkout(_prices, _offers);
     checkout.Scan("A");
     checkout.Scan("A");
     var actual = checkout.Total();
     Assert.AreEqual(100, actual);
 }
 public void One_B_should_be_30()
 {
     var checkout = new Checkout(_prices, _offers);
     checkout.Scan("B");
     var actual = checkout.Total();
     Assert.AreEqual(30, actual);
 }