Order.cs

public class Order
{
    public int OrderID { get; set; }

    public string Name { get; set; }

    public DateTime CreateAt { get; set; } 
}

public interface IOrderDao
{
    Order Get(int orderId);

    void Update(Order order);
}

public interface IIocContainer
{
    T Resolve<T>();
}

public class DefaultIocContainer : IIocContainer
{
    public readonly static DefaultIocContainer Instance = new DefaultIocContainer();

    public T Resolve<T>()
    {
        throw new NotImplementedException();
    }
}

public static class OrderLogicExtension
{
    private static IIocContainer _iocContainer;

    public static IIocContainer IocContainer
    {
        get { return _iocContainer ?? DefaultIocContainer.Instance; }
        set { _iocContainer = value; }
    }

    public static void Resubmit(this Order order)
    {
        // do something
        var dao = IocContainer.Resolve<IOrderDao>();
        dao.Update(order);
    }
}

class Program
{
    static void Main(string[] args)
    {
        // use
        var order = new Order();
        order.Resubmit();
    }

    public void ResubmitTest()
    {
        var mockDao = new Mock<IOrderDao>();
        // setup dao mock

        // setup IOC container
        var mockIocContainer = new Mock<IIocContainer>();
        mockIocContainer.Setup(c => c.Resolve<IOrderDao>()).Returns(mockDao.Object);
        OrderLogicExtension.IocContainer = mockIocContainer.Object;

        // do
        var order = new Order();
        order.Resubmit();

        // verify
    }
}