Verify that a property has been set with Moq

Question

I'm trying to learn how to use Moq and can't get this to work: I have an interface with a TextBox and a Presenter class using that interface. I want to be able to check that some method in that class has set the text property of the TextBox with a particular value. This is what I've tried:

public interface IView { TextBox MyTextBox { get; } }

public class Presenter
{
   private IView _view;

   public Presenter(IView view)
   { _view = view; }

   public void Foo(string txt)
   {
    // try to set the Text in MyTextBox:
    // this gives a NullReferenceException => _view.MyTextBox.Text = txt;           
   }
}

In my test I want to do something like this:

[Test]
public void Test_For_TestBoxText_Set()
{
   var mockView = new Mock<IView>();
   var presenter = new Presenter(mockView.Object);
   presenter.Foo("bar");
   mockView.VerifySet(v => v.MyTextBox.Text = "bar");
}

` Can anybody point me in the right direction and also explain why this is not working?

I think this could help http://stackoverflow.com/a/1642192/1363 — Ron Harlev, Mar 28 '16 at 21:30

score 1 · Accepted Answer · answered Mar 28 '16 at 21:36

1

You can create a real TextBox and make the mock return it. Then in the assert phase, you can test against that real TextBox. Here is an example:

//Arrange
Mock<IView> moq = new Mock<IView>();

var textbox = new TextBox();

moq.Setup(x => x.MyTextBox).Returns(textbox);

Presenter presenter = new Presenter(moq.Object);

//Act
presenter.Foo("test");

//Assert
Assert.AreEqual("test", textbox.Text);

answered Mar 28 '16 at 21:36

Yacoub Massad

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I've tried your solution: it works! I've tested it a bit further by changing the property type to string and then also the SetupSet/VerifySet worked. So it seems that the property SetupSet only works with primitive types and not with reference types, is that correct? Thanks a lot. – wosi Mar 29 '16 at 14:30
I am not sure I understand. What didn't work? Which property you changed to string? – Yacoub Massad Mar 29 '16 at 14:32
You misunderstood: everything worked. I only investigated a little further by changing the type of the property declared in the interface from TextBox to string. Then I could also use SetupSet without any error. So apparently that NullReferenceException I've experienced only gets thrown when you use a reference type (e.g. like TextBox), right ? – wosi Mar 29 '16 at 15:16
It seems that Moq does not auto-mock return values of properties and methods of mocked interfaces. I am not sure if and how this behavior can be changed. – Yacoub Massad Mar 31 '16 at 21:30

Verify that a property has been set with Moq

1 Answers1