DateTime.Now i podróż w czasie

DateService1.cs

public class DateService : IDateService
{
    public DateTime Now
    {
        get
        {
            return DateTime.Now;
        }
    }
 
    public DateTime UtcNow
    {
        get
        {
            return DateTime.UtcNow;
        }
    }
}

DateService2.cs

public class DateService : IDateService
{
    private TimeSpan _offset = new TimeSpan();
 
    public DateTime Now
    {
        get
        {
            return DateTime.Now + _offset;
        }
    }
 
    public DateTime UtcNow
    {
        get
        {
            return DateTime.UtcNow + _offset;
        }
    }
 
    public void SetNow(DateTime date)
    {
        _offset = date - DateTime.Now;
    }
 
    public void Reset()
    {
        _offset = new TimeSpan();
    }
}

IDateService.cs

public interface IDateService
{
    DateTime Now { get; }
 
    DateTime UtcNow { get; }
}

UserLogic1.cs

public User Update(User user)
{
    user.UpdatedDate = DateTime.Now;
 
    //zapis użytkownika
 
    return user;
}

UserLogic2.cs

public User Create(string name)
{
    if (DateTime.Now < new DateTime(2017, 9, 1))
    {
        throw new Exception("Rejestracja użytkowników jest zamknięta do 1 września 2017.");
    }
 
    User user = new User();
 
    user.Name = name;
 
    //dodanie użytkownika
     
    return user;
}

UserLogic3.cs

public class UserLogic
{
    private IDateService _dateService;
 
    public UserLogic(IDateService dateService)
    {
        _dateService = dateService;
    }
 
 
    public User Update(User user)
    {
        user.UpdatedDate = _dateService.Now;
 
        //zapis użytkownika
 
        return user;
    }
}

UserLogicTests.cs

[TestFixture]
public class UserLogicTests
{
    private Mock<IDateService> _dateServiceMock;
 
    private UserLogic Create()
    {
        _dateServiceMock = new Mock<IDateService>();
 
        return new UserLogic(_dateServiceMock.Object);
    }
 
    [Test]
    public void Update_SetUpdatedDate()
    {
        var userLogic = Create();
 
        _dateServiceMock.Setup(u => u.Now)
            .Returns(new DateTime(2017, 1, 1));
 
        var user = userLogic.Update(new User());
 
        Assert.AreEqual(new DateTime(2017, 1, 1), user.UpdatedDate);
    }
}