Mocking DateTime

Question

public void DoSomethingAccordingToYear()
{
    if(DateTime.Now.Year < 2010)
        DoSomething();
    else
        DoSomethingElse();
}

I want to test this method. How can I mock DateTime without changing my code and without using interfaces?

Neither of those options allow you to run tests automatically, please don't do that! — DavidG, Jul 24 '17 at 11:48
Also @TejashwiKalpTaru the `DateTime` object is immutable, you can't change it. — DavidG, Jul 24 '17 at 11:55
I would use different signature for testing/debuging [like this](http://rextester.com/XXZI58594) — mrogal.ski, Jul 24 '17 at 12:04
You can also try using the virtual time from package Install-Package VirtualTime — Samuel, Mar 20 '18 at 00:15

score 4 · Answer 1 · answered Jul 24 '17 at 11:47

One common way to do this is to pass in a component that gets the date. For example:

public interface IDateTimeNowProvider
{
    DateTime Now { get; }
}

public class DateTimeNowProvider : IDateTimeNowProvider
{
    public DateTime Now => DateTime.Now;
}

Now you can inject a IDateTimeNowProvider into your object and mock that instead.

Romano Zumbé · Answer 2 · 2017-07-24T11:53:08.993

If you change the definition of your method it would be simple:

public void DoSomethingAccordingToYear(DateTime testDate)
{
    if(testDate.Year < 2010)
        DoSomething();
    else
        DoSomethingElse();
}

Then call it like this:

// production
DoSomethingAccordingToYear(DateTime.Now);

// test
DoSomethingAccordingToYear(new DateTime(2009,1,1));

EDIT

If you don't want to change the way you call the method, you could also implement it like this:

public void DoSomethingAccordingToYear(DateTime? testDate = null)
{
    testDate = testDate ?? DateTime.Now;

    if (testDate.Year < 2010)
        DoSomething();
    else
        DoSomethingElse();
}

If you would call it without a parameter then it would use DateTime.Now but you can still pass a parameter for testing.

Mocking DateTime

2 Answers2