OrderServiceTest2.cs

using Microsoft.VisualStudio.TestTools.UnitTesting;
using NSubstitute;
using System;
using System.Collections.Generic;
using System.Data.Linq;
using System.Linq;

namespace UnitTestProject8
{
    [TestClass]
    public class UnitTest1
    {
        [TestMethod]
        public void TestMethod1()
        {
            var model = Substitute.For<IOrderModel>();

            var orderService = new OrderService(model);
            List<string> names = new List<string> { "Book", "Table", "Pen", "Mouse" };

            // Act
            orderService.CreateOrdersByNames(names);

            model.Received(1).Add(orders: Arg.Is<List<OrderDomain>>(orders =>
                orders.Count() == 4 &&
                orders[0].Name == "Book" &&
                orders[1].Name == "Table" &&
                orders[2].Name == "Pen" &&
                orders[3].Name == "Mouse"));
        }
    }

    public class OrderService
    {
        private readonly IOrderModel _model;

        public OrderService(IOrderModel model)
        {
            _model = model;
        }

        public void CreateOrdersByNames(List<string> names)
        {
            var orders = names.Select(name => new OrderDomain(name)).ToList();
            _model.Add(orders);
        }
    }

    public class OrderDomain
    {
        public string Name { get; }

        public OrderDomain(string name)
        {
            Name = name;
        }
    }

    public interface IOrderModel
    {
        void Add(List<OrderDomain> orders);
        void Add(OrderDomain orderDomain);
    }

    public class OrderModel : IOrderModel
    {
        public void Add(OrderDomain orderDomain)
        {
            Add(new List<OrderDomain> { orderDomain });
        }

        public void Add(List<OrderDomain> orders)
        {
            foreach (OrderDomain item in orders)
            {
                new Order(item.Name).Save();
            }
        }
    }

    /// <summary>
    /// Mapping Database's Table : ORDER
    /// </summary>
    public class Order : BaseTableObject
    {
        private string _Name;
        private DateTime _CreateDate;
        public Order(string name)
        {
            _Name = name;
            _CreateDate = DateTime.Now;
        }

        public void Save()
        {
            string sql = "INSERT INTO ORDER .... ";
            dataContext.ExecuteCommand(sql);
        }
    }

    public class BaseTableObject
    {
        protected DataContext dataContext;
        public BaseTableObject()
        {
            dataContext = new DataContext("Connection String........");
        }
    }
}