Question

I am using Moq, NUnit, WPF, MVVM, Ninject.

I am writing a test for my LoginViewModel, and in the test when I use the constructor of the LoginViewModel to create a new instance, I am getting a NullReferenceException error. The code compiles and runs, (i.e. when I run the program the LoginView shows, and works with the LoginViewModel to create the correct behaviour etc) but for some reason the UnitTest is crashing.

this is the constructor:

public LoginViewModel(ILoginServices loginServices,IDialogService dialogServices)
{
            InitializeFields();
            _loginServices = loginServices;
            _dialogService = dialogServices;
            DomainList = _loginServices.GetDomainListing();

}

I have mocked the dependencies as follows:

Mock<ILoginServices> moq = new Mock<ILoginServices>();
 moq.Setup(log =>
           log.LoginUser(It.IsAny<string>(), 
                         It.IsAny<string>(), 
                         It.IsAny<string>()))
           .Callback<string, string, string>((i, j, k) => CheckArgs(i, j, k));

 moq.Setup(log2 =>
           log2.GetDomainListing()).Returns(new List<string> { "Domain" });

 Mock<IDialogService> moq2 = new Mock<IDialogService>();

• I have also tried inserting real services as the parameters.
• I have verified that the mocks do work, and the objects these mocks
  return are not null.
• I have commented out all the code in the constructor.

• I have tried inserting the line

  LoginViewModel test = new LoginViewModel(_fakeLoginService,_fakeDialogService);

  in front of the call to the constructor (to see if it had to do with the original local variable being disposed or something before) and this line crashed instead.

From all I can see this must be the constructor,(but not the code I have written inside it) and that this is solely related to NUnit / Moq as my code still compiles and runs fine.

I have no idea on this one guys, can anyone point me in the right direction?

---

[Edit]

Ok so I have run through the code and the error comes from this line of code:

ImageSource = (ImageSource)Application.Current.FindResource(_imageName);

This code is going to a ImageDictionary and getting a reference to the image for an undo button in the WindowViewModel (which my LoginViewModel inherits).

My hypotheses as to why its working in the normal running of the application, but not in the testing are:

1) Because I am running the program code through NUnit, the Application.Current object isnt getting property assigned/there is no Application.Current object to get.

                                  **or**

2) Something to do with the fact that because the program code is being run in NUnit, the code doesn’t have access to/can’t resolve the ImageDictionary to find the image.

I’m leaning more strongly to the first hypothesis, but I’m as of yet not 100% sure, and I am having trouble finding the values of the Application.Current at runtime, cause when I move my cursor over the code the tooltip that normally appears showing the detail of the object that is not appearing.

My new question is: Does any of this make sense? Do you guys know if the Application.Current object exists / can be accessed when running the testing project through NUnit?

Any help will be appreciated.

Answer 1

You are correct. Application.Current is null for Unit tests. You can work around this by injecting the Application object as referencing singletons in code can make life tricky.