public class MockUserRepository
    {
        private readonly IList<User> _users;

        public MockUserRepository()
        {
            _users = new List<User>()
                         {
                             new User()
                                 {
                                     UserId = new Guid("E480E40F-6802-4296-B2A8-E0D5E018CD41"),
                                     Username = "admin",
                                     Password = "5A105E8B9D40E1329780D62EA2265D8A",
                                     CellPhone = "3175172957"
                                 }
                         };
        }

        public IUserRepository Create()
        {
            var mockUserRepository = new Mock<IUserRepository>();

            mockUserRepository.Setup(m => m.Count()).Returns(_users.Count());

            mockUserRepository.Setup(m => m.Get()).Returns(_users);

            mockUserRepository.Setup(m => m.Get(It.IsAny<Guid>())).Returns((Guid id) => _users.First(x => x.UserId == id));

            mockUserRepository.Setup(m => m.Save(It.IsAny<User>())).Returns(
                (User user) =>
                    {
                        var now = DateTime.Now;

                        user.ModifiedOn = now;

                        if(user.UserId.Equals(Guid.Empty))
                        {
                            user.CreatedOn = now;
                            _users.Add(user);
                        }
                        else
                        {
                            var original = _users.First(x => x.UserId == user.UserId);
                            if (original == null)
                            {
                                return false;
                            }

                            original = user;
                        }
                        return true;
                    }
                );

            mockUserRepository.Setup(m => m.Find(It.IsAny<IList<object[]>>())).Returns(
                (IList<object[]> criteria) =>
                {
                    IList<User> uList = _users.ToList();

                    foreach (object[] criteriaItem in criteria)
                    {
                        var name = (string)criteriaItem[0];
                        var value = (string)criteriaItem[1];
                        IList<User> tempList = uList.ToList();
                        IList<User> addList = tempList.Where(user => (string) user.GetType().GetProperty(name).GetValue(user, null) == value).ToList();
                        uList = addList;
                    }
                    return uList;
                });

            return mockUserRepository.Object;
        }
    }

public class MockUserRepository : IUserRepository

[SetUp]
    public void Setup()
    {
        MockUserRepository = new MockUserRepository().Create();
        MockRoleRepository = new MockRoleRepository().Create();
        MockQuestionRepository = new MockQuestionRepository().Create();

        AuthenticationService = new AuthenticationService(MockUserRepository, MockRoleRepository, MockQuestionRepository);
    }

reposistory = new Mock<IUserRepository>();

var id = 1;
var user = new User();
repository.Setup(x=> x.Get(id)).Returns(user);

var sut = new Service(repository.Object);
var result = sut.Get(id);

Assert.Equals(user, result);

class FakeUserRepository : IUserRepository
{
    public List<User> Users = new List<Users>();

    public User Get(long id)
    {
         return Users.FristOrDetail(x=>x.Id = id);
    }
}

var id = 1;
var user = new User();
var repository = new FakeUserRepository();
repository.Users.Add(user);

var sut = new Service(repository);
var result = sut.Get(id);

Assert.Equals(user, result);