What's a good way to overwrite DateTime.Now during testing?

Question

I\'ve got some (C#) code that relies on today\'s date to correctly calculate things in the future. If I use today\'s date in the testing, I have to repeat the calculation in

Answer 1

Using Microsoft Fakes to create a shim is a really easy way to do this. Suppose I had the following class:

public class MyClass
{
    public string WhatsTheTime()
    {
        return DateTime.Now.ToString();
    }

}

In Visual Studio 2012 you can add a Fakes assembly to your test project by right clicking on the assembly you want to create Fakes/Shims for and selecting "Add Fakes Assembly"

Finally, Here is what the test class would look like:

using System;
using ConsoleApplication11;
using Microsoft.QualityTools.Testing.Fakes;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace DateTimeTest
{
[TestClass]
public class UnitTest1
{
    [TestMethod]
    public void TestWhatsTheTime()
    {

        using(ShimsContext.Create()){

            //Arrange
            System.Fakes.ShimDateTime.NowGet =
            () =>
            { return new DateTime(2010, 1, 1); };

            var myClass = new MyClass();

            //Act
            var timeString = myClass.WhatsTheTime();

            //Assert
            Assert.AreEqual("1/1/2010 12:00:00 AM",timeString);

        }
    }
}
}