How do i Unit Test my RelayCommand using Moq?

Question

I have a RelayCommand Class which implements the ICommand interface and it takes a new Action as the parameter for its constructor. It is pretty basic

For example here is how i use command when a button is clicked. And this code is in the constructor of my ViewModel.

All this code does is opens a FolderBrowserDialog and lets the user select a folder.

OutputSelect = new RelayCommand(new Action<object>(folderSelect));

This is a method in the viewModel class

public void folderSelect(object obj)
        {
            var dlg = new FolderBrowserDialog();


            Nullable<bool> result = dlg.ShowDialog();

            if (result == true)
            {
                // Open document             
                string filename = dlg.SelectedPath;
                _model.OutputFolder = filename;
            }
        }

Once the button is clicked the method folderSelect is run.

Now I am wondering how do I unit test this feature of my Application?

Do i make a Mock for a Action and pass that into my viewModel.OutputSelect.Execute()?

why not sub-class it? make a service to show folder dialog (this only shows the folder browser, so doesn't need to be unit tested). VM can have dependency on this selection service and you unit test it with mocked interface. You don't need to see the FolderBrowserDialog in your test or verification — is_this_the_way

Aditya Potdar Aditya Potdar · Accepted Answer · 2014-11-03T15:06:08

"Model View ViewModel" is an architectural pattern and which give us clear separation between User interface layer (UI) to Business Layer. The Button Command Property is of ICommand Type and behind the scenes when user click on the Button it called ICommand.Execute() method.

So, to do unit testing you can do this by direct calling of Execute(object parameter) method In you case it is

OutputSelect.Execute(null)

How do i Unit Test my RelayCommand using Moq?

1 Answers