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

using NHibernate;
using Northwind.DataAccess;
using Northwind.DataAccess.Repository;
using Northwind.Domain;
using Northwind.Domain.Model;
using Northwind.TransferObjects.Model;
using Northwind.TransferObjects.Presentation;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;

namespace Northwind.Services
{
    /// <summary>
    /// Implements a Service Pattern for customer management
    /// </summary>
    public class CustomerServices : ICustomerServices
    {
        IRepository<Customer, string> customerRepository;
        ISessionFactory sessionFactory;

        public CustomerServices()
        {
            DataAccessHelper.Initialize();
            sessionFactory = DataAccessHelper.SessionFactory;
        }

        public CustomerServices(RepositoryMode repositoryMode) : this(repositoryMode, DataAccessHelper.SessionFactory){}

        public CustomerServices(RepositoryMode repositoryMode, ISessionFactory sessionFactory)
        {
            DataAccessHelper.Initialize();
            switch (repositoryMode)
            {
                case RepositoryMode.Database:
                    customerRepository = new CustomerRepository();
                    break;
                case RepositoryMode.InMemory:
                    customerRepository = new InMemoryCustomerRepository();
                    break;
            }
            this.sessionFactory = sessionFactory;
        }

        public CustomerServices(IRepository<Customer,string>  customerRepository, ISessionFactory sessionFactory)
        {
            DataAccessHelper.Initialize();
            this.customerRepository = customerRepository;
            this.sessionFactory = sessionFactory;
        }

        public CustomerTO GetDetailsForCustomer(string id)
        {
            Customer customer = customerRepository.Load(id);
            return (CustomerTO)TOHelper<Customer>.GetTO(typeof(CustomerTO), customer);
        }

        public void UpdateCustomer(CustomerTO customerTO)
        {
            try
            {
                Customer customer = customerRepository.Load(customerTO.ID);

                Order o = new Order();
                o.CustomerID = customer.ID;
                o.EmployeeID = 3;
                o.ShipVia = 1;
                customer.Orders.Add(o);

                TOHelper<Customer>.UpdateDomainFromTO(customerTO, customer);

                using (ISession session = sessionFactory.OpenSession())
                {
                    using (ITransaction transaction = session.BeginTransaction())
                    {
                        customerRepository.AddOrUpdate(session, customer);
                        transaction.Commit();
                    }
                }
            }
            catch
            {
                throw;
            }
        }

        public CustomerTO NewCustomer(string customerId)
        {
            Customer c = new Customer();
            c.ID = customerId;
            //c.Address = "";
            //c.City = "";
            c.CompanyName = "[COMPANY NAME]";
            //c.ContactName = "";
            //c.ContactTitle = "";
            //c.Country = "";
            //c.Fax = "";
            c.Phone = "[PHONE NUMBER]";
            //c.PostalCode = "";
            //c.Region = "";
            using (ISession session = sessionFactory.OpenSession())
            {
                using (ITransaction transaction = session.BeginTransaction())
                {
                    customerRepository.AddOrUpdate(session, c);
                    transaction.Commit();
                }
            }
            return (CustomerTO)TOHelper<Customer>.GetTO(typeof(CustomerTO), c);
        }

        public void DeleteCustomer(string customerId)
        {
            Customer c = new Customer();
            c.ID = customerId;
            using (ISession session = sessionFactory.OpenSession())
            {
                using (ITransaction transaction = session.BeginTransaction())
                {
                    customerRepository.Remove(session, c);
                    transaction.Commit();
                }
            }
        }

        public ILookupCollection GetCustomerList()
        {
            Customer c = new Customer();
            Customer[] customers = customerRepository.FetchByExample(c);
            List<object> toList = (List<object>)TOHelper<Customer>.GetTO(typeof(CustomerTO), customers);
            return new LookupCollection(new CustomerToLookupConverter().ConvertAllFrom(toList));
        }

        public ILookupCollection GetCustomerList(string name)
        {
            Customer[] customers = ((CustomerRepository)customerRepository).FetchByName(name);
            List<object> toList = (List<object>)TOHelper<Customer>.GetTO(typeof(CustomerTO), customers);
            return new LookupCollection(new CustomerToLookupConverter().ConvertAllFrom(toList));
        }
    }

    public enum RepositoryMode
    {
        Database,
        InMemory
    }
}