OpenDoor1.cs

// code that's 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;
        }

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

        return total;
    }
}


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


[TestClass]
public class CheckoutTests
{
    [TestMethod]
    public void CalculateCostTest()
    {
        var orders = new List<Order>();

        orders.Add(new Order() { Drink = "Little Creatures Pale Ale", Quantity = 2 });
        orders.Add(new Order() { Drink = "Pigs Fly Pale Ale", Quantity = 1 });
        orders.Add(new Order() { Drink = "Hitachino White Ale", Quantity = 1 });

        var checkout = new Checkout();

        // Little Creatures Pale Ale - $7
        // Pigs Fly Pale Ale - $8
        // Hitachino White Ale - $9
        Assert.AreEqual(34.10m, checkout.CalculateCost(orders));
    }
}