OpenDoor2.cs

// code that's extremely difficult to test

public class Checkout
{
    public decimal CalculateCost(List<Order> orders)
    {
        // get the price list
        var drinksMenu = getDrinksMenu();

        var total = 0.0m;

        // total the orders
        foreach(var order in orders)
        {
            total += drinksMenu.LookupPrice(order.Drink) * order.Quantity;
        }

        // half price on Friday 5pm-6pm
        var dateTimeNow = DateTime.Now;
        if (dateTimeNow.DayOfWeek == DayOfWeek.Friday && dateTimeNow.Hour == 17)
        {
            total /= 2;
        }

        // calculate the tax
        total += total * 0.1m;

        return total;
    }
}


public class Order
{
    public string Drink { get; set; }
    public int Quantity { get; set; }
}