Question

I’m trying to write a unit test for a sample project that uses the MVP architecture.
When I run the test, I have the following error message:

UnitTests.Tests.testCopy:
Expected: “Testing …”
But was: null

I post below the snippets I did:

namespace Copy
{
    public interface IView
    {
        string Copy { get; set; }
        string Original { get; }
        event EventHandler Changed;
    }

    public class Presenter
    {
        private IView view;
        public Presenter(IView view)
        {
            this.view = view;
            this.view.Changed += new EventHandler(OnChanged);
        }

        public void OnChanged(object sender, EventArgs e)
        {
            view.Copy = view.Original;
        }
    }

    public partial class Form1 : Form, IView
    {
        private Presenter presenter;

        public Form1()
        {
            InitializeComponent();
            presenter = new Presenter(thisIView);
            this.t_originalviewMock.TextChanged += OnChanged;
        }

        public string Original
        {
            get { return t_originalMockInstance).Text; }
        }

        public string Copy
        {
            get { return t_copy.Text; }
            set { t_copy.Text = value;}
        }

        private void OnChanged(object sender, EventArgs e)
        {
            if (Changed != null)
                Changed(sender, e);
        }

        public event EventHandler Changed;
    }
}

Unit test code:

namespace UnitTests
{
    [TestFixture]
    public class Tests
    {
        private DynamicMock viewMock;
        private Presenter presenter;

        [SetUp]
        public void setup()
        {
            viewMock = new DynamicMock(typeof(IView));
            presenter = new Presenter((IView)viewMock.MockInstance);
        }

        [Test]
        public void testCopy()
        {
            viewMock.ExpectAndReturn("get_Original", "Testing ...");
            viewMock.Expect("get_Cpoy");
            Assert.AreEqual("Testing ...", 
                ((IView)viewMock.MockInstance).Copy);
        }
    }
}

Thank you for your help.

Answer 1

“I’m trying to test that a change in Original textBox, leads to a change in Copy textBox.”

Here’s how you should set up your test then:

1. Tell view mock to raise Changed event
2. Tell view mock to return "Testing ..." upon call to get_Original property getter
3. Tell view mock you’re expecting call to Copy setter with "Testing ..." value
4. Verify mock expectations

I’m not sure whether raising events is possible with NUnit.Mocks. Judging by fairly tiny API, I’d say no. Yet you can go around this problem by invoking event handler directly (since it’s public anyways):

viewMock.ExpectAndReturn("get_Original", "Testing ...");
viewMock.Expect("set_Copy", "Testing ...");

presenter.OnChanged(viewMock, EventArgs.Empty);

// here we verify expectations set on mock object; 
// that Copy setter was called with "Testing ..." value
viewMock.Verify();

You can see that this test indeed works by simply changing set_Copy expected value to something else than "Testing ..." – it will fail with appropriate message.

Mocking frameworks sidenote

Any reason you’re using NUnit.Mocks instead of more serious mocking framework? Give FakeItEasy, Moq or RhinoMocks a look.

This is how your test could look like if you’d used FakeItEasy instead:

[Test]
public void WhenViewChangedEventIsRaised_PresenterSetsCopyProperty()
{
    var viewMock = A.Fake<IView>();
    var presenter = new Presenter(viewMock);
    A.CallTo(() => viewMock.Original).Returns("Testing ...");

    viewMock.Changed += Raise.With(EventArgs.Empty).Now;

    Assert.AreEqual(viewMock.Copy, "Testing ...");
}

Note that problems like typing Cpoy instead of Copy immediately go away. Not to mention you won’t have to make your event handlers exposed in public API.