Exception in dialog causes MSTest to crash

Question

I'm researching some behaviour in our application and made a test that consistently makes the test engine crash. I simplified the test code into this:

[TestMethod, Timeout(2000)]
public void ShowDialogShouldCleanupAfterException()
{
    var topWindow = new Window();

    topWindow.Loaded += (sender, args) =>
    {
        var childWindow = new Window();
        childWindow.Loaded += (o, eventArgs) =>
        {
            throw new Exception("ChildWindowException");
        };

        childWindow.ShowDialog();
        topWindow.Close();
    };

    topWindow.ShowDialog();
}

Everytime I run this code a dialog pops up telling me vstest.executionengine.exe has stopped working. Why is this happening and can I do something to make sure the test keeps running when this happens?

EDIT

Similar behaviour occurs in a WPF Sample application:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        Loaded += MainWindow_Loaded;
    }

    private void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        var childWindow = new Window();
        childWindow.Loaded += ChildWindow_Loaded;
        childWindow.Owner = this;
        try
        {
            childWindow.ShowDialog();
        }
        catch (Exception)
        {
            MessageBox.Show("Exception caught");
        }
    }

    private void ChildWindow_Loaded(object sender, RoutedEventArgs e)
    {
        throw new NotImplementedException();
    }
...

I understand this code has problems. Catching the exception in the child dialog would solve this. But I'm simply trying to understand why it behaves like this.

It often happen due to recursive calls. Possible duplicate of https://stackoverflow.com/questions/40150167/vstest-crashed-when-running-some-particular-tests — Abhishek K. Upadhyay, Jul 25 '17 at 12:18
I wouldn't expect a test runner to have set up the necessary infrastructure for UI to run. — Damien_The_Unbeliever, Jul 25 '17 at 12:30
@Damien_The_Unbeliever, good suggestion but my other tests featuring UI components just work and I have similar behaviour in a WPF application. That's the reason I'm making these unuasal tests. I edited my question with an example of this in a WPF application. — Martijn, Jul 25 '17 at 12:44

score 0 · Accepted Answer · answered Jul 25 '17 at 13:40

Ok, I eventually found out why this happens and a way to solve it in my application.

Exceptions that happen in a different dispatcher, need to be handled on that dispatcher. The exception bubbles up the stack. The stack of a sub dialog starts after the ShowDialog is called. So any exceptions happening in that dialog, will not just be caught by a try/catch of the calling code. These exceptions need to be specifically handled.

In this question about handling exceptions in wpf, I found out that I can handle these exceptions with the following code:

childWindow.Dispatcher.UnhandledException += (o, eventArgs) =>
{
   // handling code...
    eventArgs.Handled = true;
};

This is how I understood it. Please correct me if I'm wrong!

Exception in dialog causes MSTest to crash

1 Answers1