Moq does not take a snapshot of parameters passed into a mocked method, and any mutation after the 'Act' stage of a test will be picked up if the object reference is used in a callback from a later Verify statement. The below test unexpectedly fails.

gistfile1.cs

using Moq;

using NUnit.Framework;

namespace MockTester
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;

    public class Test
    {

        [Test]
        public void TheUnitTest()
        {
            var mockedDao = new MockRepository(MockBehavior.Loose).Create<IDao>();
            var sut = new PersonService(mockedDao.Object);
            IList<string> names = new[] { "James", "Ken" }.ToList();

            sut.CreatePeople(names);


            // Note that "Paul" is added AFTER the action (and thus when
            // the mock recorded invocation with it....
            names.Add("Paul");

            mockedDao.Verify(d=>d.SaveItems(It.Is<IList<String>>(l => PaulIsInList (l))), Times.Never);
        }

        private bool PaulIsInList(IList<string> list)
        {
            return list.Contains("Paul");
        }
    }

    public class PersonService
    {
        private readonly IDao _mockedDao;

        public PersonService(IDao mockedDao)
        {
            _mockedDao = mockedDao;
        }

        public void CreatePeople(IList<String> names)
        {
            _mockedDao.SaveItems(names);
        }
    }

    public interface IDao
    {
        void SaveItems(IList<String> names);
    }
}