Any alternative for Microsoft Fakes in .NET Core?

Question

I am looking for an alternative to Microsoft Fakes in .NET Core. I know it is no longer supported in .NET Core. I just do not understand why not, I think it was a good solution in certain situations.

My problem is that I want to mock DateTime.Now. Previously you could do this with the following code:

System.Fakes.ShimDateTime.NowGet = () => 
{ 
   return new DateTime(2000, 1, 1); 
};

It is described in the Microsoft documentation, see the link for more information: https://docs.microsoft.com/en-us/visualstudio/test/using-shims-to-isolate-your-application-from-other-assemblies-for-unit-testing?view=vs-2017

For now I solved it by creating a wrapper for DateTime, which looks like this:

/// <summary>
/// Used for getting DateTime.Now(), time is changeable for unit testing
/// </summary>
public static class SystemTime
{
   /// <summary> 
   /// Normally this is a pass-through to DateTime.Now, but it can be 
   /// overridden with SetDateTime( .. ) for testing or debugging.
   /// </summary>
   public static Func<DateTime> Now = () => DateTime.Now;

   /// <summary> 
   /// Set time to return when SystemTime.Now() is called.
   /// </summary>
   public static void SetDateTime(DateTime dateTimeNow)
   {
      Now = () =>  dateTimeNow;
   }

   /// <summary> 
   /// Resets SystemTime.Now() to return DateTime.Now.
   /// </summary>
   public static void ResetDateTime()
   {
       Now = () => DateTime.Now;
   }
}

I owe this solution to the next StackOverflow post: Unit Testing: DateTime.Now

But I am not satisfied with this solution yet, because I feel I have to adjust my implementation for my testing. I do not think this is desirable.

I hope someone can help me with this, thanks in advance for the effort.

Answer 1

Pose works well for this.

using Pose;

Shim dateTimeShim = Shim.Replace(() => DateTime.Now).With(() => new DateTime(2004, 4, 4));

// This block executes immediately
PoseContext.Isolate(() =>
{
    // All code that executes within this block
    // is isolated and shimmed methods are replaced

    // Outputs "4/4/04 12:00:00 AM"
    Console.WriteLine(DateTime.Now);

}, dateTimeShim);