How design patterns can help you in developing unit testing-enabled applications

using Castle.ActiveRecord;
using Castle.ActiveRecord.Framework;
using Castle.ActiveRecord.Queries;
using NHibernate;
using NHibernate.Expression;
using Northwind.Domain;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;

namespace Northwind.Domain.Model
{
    /// <summary>
    /// This domain model class is mapped to the Customers table of Northwind database for Castle Project ActiveRecorrd framework.
    /// Besides, it is also mapped to the CustomerTO transfer class.
    /// </summary>
    [ActiveRecord("Customers")]
    [MappedTO("Northwind.TransferObjects.Model.CustomerTO")]
    public class Customer : DomainBase<string>
    {
        string customerID;
        string address;
        string city;
        string companyName;
        string contactName;
        string contactTitle;
        string country;
        string fax;
        string phone;
        string postalCode;
        string region;
        IList orders = new List<object>();

        public Customer()
        {
        }

        public override bool Equals(object obj)
        {
            if (obj is Customer)
            {
                bool ret = false;
                Customer objComp = (Customer)obj;
                ret =
                (objComp.ID == this.ID);
                return ret;
            }
            else
            {
                return false;
            }
        }

        public override int GetHashCode()
        {
            return base.GetHashCode();
        }

        [PrimaryKey(Column = "CustomerID", Generator = PrimaryKeyType.Assigned)]
        public override string ID
        {
            get { return customerID; }
            set {
                    if (customerID != value)
                    {
                        IsDirty = true;
                    }
                    customerID = value;
                }
        }

        [Property()]
        public string Address
        {
            get { return address; }
            set
            {
                if (address != value)
                {
                    IsDirty = true;
                }
                address = value;
            }
        }

        [Property()]
        public string City
        {
            get { return city; }
            set
            {
                if (city != value)
                {
                    IsDirty = true;
                }
                city = value;
            }
        }

        [Property()]
        public string CompanyName
        {
            get { return companyName; }
            set
            {
                if (string.IsNullOrEmpty(value))
                    throw new EmptyValueException("CompanyName");

                if (companyName != value)
                {
                    IsDirty = true;
                }
                companyName = value;
            }
        }

        [Property()]
        public string ContactName
        {
            get { return contactName; }
            set
            {
                if (contactName != value)
                {
                    IsDirty = true;
                }
                contactName = value;
            }
        }

        [Property()]
        public string ContactTitle
        {
            get { return contactTitle; }
            set
            {
                if (contactTitle != value)
                {
                    IsDirty = true;
                }
                contactTitle = value;
            }
        }

        [Property()]
        public string Country
        {
            get { return country; }
            set {
                if (country != value)
                {
                    IsDirty = true;
                }
                country = value; 
                }
        }

        [Property()]
        public string Fax
        {
            get { return fax; }
            set
            {
                if (fax != value)
                {
                    IsDirty = true;
                }
                fax = value;
            }
        }

        [Property()]
        public string Phone
        {
            get { return phone; }
            set
            {
                if (string.IsNullOrEmpty(value))
                    throw new EmptyValueException("Phone");
                if (phone != value)
                {
                    IsDirty = true;
                }
                phone = value;
            }
        }

        [Property()]
        public string PostalCode
        {
            get { return postalCode; }
            set
            {
                if (postalCode != value)
                {
                    IsDirty = true;
                }
                postalCode = value;
            }
        }

        [Property()]
        public string Region
        {
            get { return region; }
            set
            {
                if (region != value)
                {
                    IsDirty = true;
                }
                region = value;
            }
        }

        public IList Orders
        {
            get { return orders; }
            set {
                if (orders != value)
                {
                    IsDirty = true;
                }
                orders = value; 
            }
        }
    }
}