public void Clear_AddValidItemToCartThenClear_TotalEquals0()
{
IProductRepository products = A.Fake<IProductRepository>();
ShoppingCart shoppingCart = new ShoppingCart(products);
A.CallTo(() => products.GetProductById("item-1")).Returns(new Product("item-1", "Banana", 14.5));
shoppingCart.AddItem("item-1");
shoppingCart.Clear();
Assert.That(shoppingCart.Total, Is.EqualTo(0));
}