Question

I’m writing Unit-Tests for an OK_Execute Command in an MvvM-Scenario.

Now that’s working fine until the method calls:

        obj.DialogResult = !datumExistiertBereits || datumUeberschreiben;
        obj.Close();  

where the first line fires the following InvalidOperationException:

DialogResult can be set only after Window is created and shown as dialog.

Now I wonder how I can make my window stub object responsible to these calls without really showing the dialog in my Unit-Tests?

Thanks in advance

Steav

Answer 1

You need to move the responsability to show an actual dialog (or any window for that matter) to a seperate class, which implements an interface, and only hand an instance of that class to the VM using it.

Example:

interface IDialogService
{
  Result ShowDialog();
}

class ViewModel
{
  ViewModel( IDialogService dlgService ) { ... }

  void ExecuteSomeCommand()
  {
    var result = dlgService.ShowDialog(); 
  }
}

//actual code
class ActualDialog : IDialogService { ... }

var vm = new ViewModel( new ActualDialog() );

//test pseudocode (sorry I don't know RhinoMock)
var vm = new ViewModel( RhinoMock.GetMeAMockFor<IDialogService>() );

You can easily see the advantages this has: vm doesn’t know anything at all about the dialog and does not depend on code for showing/closing windows anymore, plus you can test the code by mocking the dialog service.