public void Create_ContainsNoProductAndZeroQuantity()
{
var np = new NoStockProduct();
Assert.Equal(0, np.Quantity);
Assert.IsType <NoProduct>(np.Product);
}
public void DecreaseStock_DoesNothing()
{
var np = new NoStockProduct();
np.DecreaseStock(10);
Assert.Equal(0, np.Quantity);
}