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 Northwind.DataAccess.Query;
using Northwind.Domain.Model;
using System;
using System.Collections.Generic;
using System.Text;

namespace Northwind.DataAccess.Repository
{
    public class InMemoryCustomerRepository : InMemoryRepositoryBase<Customer, string>, IInMemoryCustomerRepository
    {
        protected static string lastId;
        protected override object GetNextID()
        {
            return null;
        }

        public Customer[] FetchByName(string name)
        {
            FetchCustomerByNameQuery fbn = new FetchCustomerByNameQuery(name);
            Customer[] domainObjects = (Customer[])ActiveRecordBase.ExecuteQuery(fbn);
            return domainObjects;
        }

        public Customer[] FetchByNameRange(string lowerBoundName, string upperBoundName)
        {
            FetchCustomerByNameRangeQuery fbnr = new FetchCustomerByNameRangeQuery(lowerBoundName, upperBoundName);
            Customer[] domainObjects = (Customer[])ActiveRecordBase.ExecuteQuery(fbnr);
            return domainObjects;
        }

        protected override void LoadChildren(Customer customer)
        {
            OrderRepository orderRepository = new OrderRepository();
            Order orderExample = new Order();
            orderExample.CustomerID = customer.ID;
            Order[] orders = orderRepository.FetchByExample(orderExample);
            foreach (Order order in orders)
            {
                order.IsNew = false;
                order.IsDirty = false;
                customer.Orders.Add(order);
            }
        }

        protected override void AddOrUpdateChildren(ISession session, Customer customer)
        {
            InMemoryOrderRepository inMemoryOrderRepository = new InMemoryOrderRepository();
            foreach (Order order in customer.Orders)
            {
                inMemoryOrderRepository.AddOrUpdate(session, order);
            }
        }

        protected override void RemoveChildren(ISession session, Customer customer)
        {
            InMemoryOrderRepository inMemoryOrderRepository = new InMemoryOrderRepository();
            LoadChildren(customer);
            foreach (Order order in customer.Orders)
            {
                inMemoryOrderRepository.Remove(session, order);
            }
        }
    }
}