AutoFixture-based version of the Greeter class

AutoFixtureGreeterSample.cs

namespace AutoFixtureSample
{
  using System;
  using NSubstitute;
  using Ploeh.AutoFixture;
  using Ploeh.AutoFixture.AutoNSubstitute;
  using Ploeh.AutoFixture.Xunit2;
  using Xunit;

  /// <summary>
  /// That is the AutoFixture-based version of the Greeter class described by Dan Solovay here:
  /// http://www.dansolovay.com/2015/11/autofac-aggregate-service.html?showComment=1447605902217 
  /// Requires the following NuGetPackages to be installed:
  /// Install-Package xunit
  /// Install-Package AutoFixture.AutoNSubstitute
  /// Install-Package AutoFixture.Xunit2
  /// </summary>
  public class GreeterTest
  {
    [Theory, DefaultAutoData]
    public void Greeter_Hour0_WritesGoodMorning([Frozen]IDateTime fakeTime, [Frozen]IWriter writer, Greeter sut)
    {
      fakeTime.Now.Returns(new DateTime(1, 1, 1, 0, 0, 0));
      sut.WriteDate();
      writer.Received().WriteLine("Good morning");
    }

    [Theory, DefaultAutoData]
    public void Greeter_Hour13_WritesGoodAfternoon([Frozen]IDateTime fakeTime, [Frozen]IWriter writer, Greeter sut)
    {
      fakeTime.Now.Returns(new DateTime(1, 1, 1, 13, 0, 0));
      sut.WriteDate();
      writer.Received().WriteLine("Good afternoon");
    }
  }
  
  internal class DefaultAutoDataAttribute : AutoDataAttribute
  {
    public DefaultAutoDataAttribute()
      : base(new Fixture().Customize(new AutoNSubstituteCustomization()))
    {
    }
  }

  public class Greeter
  {
    private readonly IDateTime _dateTime;
    private readonly IWriter _writer;

    public Greeter(IDateTime dateTime, IWriter writer)
    {
      _dateTime = dateTime;
      _writer = writer;
    }

    public void WriteDate()
    {
      if (_dateTime.Now.Hour >= 13)
      {
        _writer.WriteLine("Good afternoon");
      }
      else
      {
        _writer.WriteLine("Good morning");
      }
    }
  }

  public interface IDateTime
  {
    DateTime Now { get; set; }
  }

  public interface IWriter
  {
    void WriteLine(string text);
  }
}