Messagebox and Unit testing

Question

I'm trying to find the best way to uncouple messageboxes from my logic so I can properly unittest it. Now I was wondering if it would be enough if I just made a seperate helper class (C#) which I can stub later for my messagebox. For instance:

static class messageBoxHelper
{
    public static void msgBoxAlg(string message, string title, MessageBoxButtons   buttons, MessageBoxIcon icons, bool show)
    {
        if (show)
        {
            MessageBox.Show(message, title, buttons, icons);
        }
 }

Then everytime I'd need to use a messagebox i'd just use messageboxHelper/msgBoxAlg(...) instead of messagebox.show(...). Using the bool show I could enable or disable it during testing.

I'm just wondering if this is the "right way". By which I mean, is there an easier or better way to do this properly? I can't just ditch the messageboxes, they relay "vital" info to the user ("Do you want to close this windows?" YES/NO etc.). It could also just be I'm not using proper software engineering, and I should decouple my messageboxes from my bussinesslogic more?

Answer 1

Yes, it is right way. But instead of static class, you should implement IDialogService and inject it into classes that should display dialogs:

public interface IDialogService
{
    void ShowMessageBox(...);

    ...
}

public class SomeClass
{
    private IDialogService dialogService;

    public SomeClass(IDialogService dialogService)
    {
       this.dialogService = dialogService;
    }

    public void SomeLogic()
    {
        ...
        if (ok)
        {
            this.dialogService.ShowMessageBox("SUCCESS", ...);
        }
        else
        {
            this.dialogService.ShowMessageBox("SHIT HAPPENS...", ...);
        }
    }
}

During testing the SomeClass you should inject mock object of the IDialogService instead of real one.

If you need to test more UI logic, consider to use MVVM pattern.

Answer 2

Look into Inversion of Control (IoC), the basic principal is that things that perform actions ect should be passed in as an interface then you use a IoC container to bind interfaces to specific implementations for your app. To easily achieve this in your case pass the thing that does message boxes in as an interface and in your unit test creat a mock (fake) version of that message box service which does not show a message box

look at http://martinfowler.com/articles/injection.html for details on IoC, my favorite container is Ninject (http://ninject.org)