Question

I am using .NET 4, NUnit and Rhino mocks. I want to unit test my news repository, but I am not sure of how to go about it. My news repository is what I will eventually be using to communicate to the database. I want to use it to test against fake/dummy data. Not sure if it is possible?? This is what I currently have:

public interface INewsRepository
{
   IEnumerable<News> FindAll();
}

public class NewsRepository : INewsRepository
{
   private readonly INewsRepository newsRepository;

   public NewsRepository(INewsRepository newsRepository)
   {
      this.newsRepository = newsRepository;
   }

   public IEnumerable<News> FindAll()
   {
      return null;
   }
}

My unit test looks like this:

public class NewsRepositoryTest
{
   private INewsRepository newsRepository;

   [SetUp]
   public void Init()
   {
      newsRepository = MockRepository.GenerateMock<NewsRepository>();
   }

   [Test]
   public void FindAll_should_return_correct_news()
   {
      // Arrange
      List<News> newsList = new List<News>();
      newsList.Add(new News { Id = 1, Title = "Test Title 1" });
      newsList.Add(new News { Id = 2, Title = "Test Title 2" });

      newsRepository.Stub(r => r.FindAll()).Return(newsList);

      // Act
      var actual = newsRepository.FindAll();

      // Assert
      Assert.AreEqual(2, actual.Count());
   }
}

In the above code I am not sure what I need to mock. The code above compiles but fails in the NUnit GUI about a contructor value. I can only assume it has to do with the INewsRepository paramter that I need to supply to NewsRepository. I don’t know how to do this in the test. Can someone please rectify my unit test so that it will pass in the NUnit GUI? Can someone also provide some feedback on if I am implementing my repositories correctly?

Being a newbie to mocking, is there anything that I need to verify? When would I need to verify? What is its purpose? I have been working through a couple of source code projects and some use verify and some don’t.

If the above test passes, what does this prove to me as developer? What does another developer have to do to my repository to make it fail in the NUnit GUI?

Sorry for all the questions, but they are newbie questions 🙂

I hope soomeone can help me out.

Answer 1

As Steven has said, you’re Asserting against the Mock NewsRepository in the above code.

The idea of mocking is to isolate the Code Under Test and to create fakes to replace their dependencies.

You use the Mock NewsRepository to test something that uses INewsRepository, in your case, you mention NewsService; NewsService will use your mock of INewsRepository.

If you search your solution for anything that uses INewsRepository.FindAll(), you will create a Mock Repository to test that code in isolation.

If you want to test something that calls your Service layer, you will need to mock NewsService.

Also, as Steven as said, there is no need for the NewsRepository to have a copy of itself injected by IoC, so:

public class NewsRepository : INewsRepository
{
   private readonly INewsRepository newsRepository;

   public NewsRepository(INewsRepository newsRepository)
   {
      this.newsRepository = newsRepository;
   }

   public IEnumerable<News> FindAll()
   {
      return null;
   }
}

should become:

public class NewsRepository : INewsRepository
{
   public IEnumerable<News> FindAll()
   {
      return null;
   }
}

Once you have functionality in your FindAll() method that needs testing, you can mock the objects that they use.

As a point of style from the great Art Of Unit Testing initialisation of mock objects is best left out of the Setup method and carried out in a helper method called at the start of the method. Since the call to Setup will be invisible and makes the initalisation of the mock unclear.

As another point of style, from that book, a suggested unit test naming convention is: “MethodUnderTest_Scenario_ExpectedBehavior“.
So,

FindAll_should_return_correct_news
could become, for example:
FindAll_AfterAddingTwoNewsItems_ReturnsACollectionWithCountOf2

I hope this makes the approach clearer.