NUnitForms: ExpectModal and MessageBoxTester

April 10, 2005

My application doesn’t want to leave anymore! I’ve seen this bug two times in two weeks, so I decided to write a non-regression test for this very simple thing, which quickly has very bad effects as the user finally ends up killing the process manually.

I usually don’t write many tests for GUI and try to focus on the underlying code (model / services) instead, but sometimes it’s really helpful. Here I’ve got a Form which asks for confirmation to the end-user, using a MessageBox.Show call:

public const string ConfirmationDialogName = "Exit?";

private void MainForm_Closing(
    object sender, 
    CancelEventArgs e)
{
    DialogResult result = MessageBox.Show(
        "Do you really want to leave?",
        ConfirmationDialogName,
        MessageBoxButtons.YesNo,
        MessageBoxIcon.Question);
    if (result == DialogResult.No)
        e.Cancel = true;
}

I’ve extracted the MessageBox name to be able to tell NUnitForms how to recognize the modal window which will open.

Now to the tests: here I inherit from NUnitFormsTest which provides some useful services such as an ExpectModal method, and I setup two tests:

one to check that answering Yes will really close the form
another one to check that answering No will leave the form opened

The two tests call ExpectModal(string modalDialogName, string modalHandler) to specify which modal dialog is expected and to specify a handler which will respond to it. Those “expectations” are automatically verified at teardown.

using System;
using Library;
using NUnit.Framework;
using NUnit.Extensions.Forms;

namespace Tests
{
    public class Tests : NUnitFormTest
    {
        MainForm form;

        public override void Setup()
        {
            base.Setup();
            form = new MainForm();
            form.Show();
        }

        [Test]
        public void CancelExitShouldNotExit()
        {
            ExpectModal(
                MainForm.ConfirmationDialogName,
                "ConfirmModalByNo");
            form.Close();
            Assert.IsFalse(form.IsDisposed);
        }

        [Test]
        public void ConfirmExitShouldExit()
        {
            ExpectModal(
                MainForm.ConfirmationDialogName,
                "ConfirmModalByYes");
            form.Close();
            Assert.IsTrue(form.IsDisposed);
        }

        public void ConfirmModalByNo()
        {
            ConfirmModal(
                MessageBoxTester.Command.No);
        }

        public void ConfirmModalByYes()
        {
            ConfirmModal(
                MessageBoxTester.Command.Yes);
        }

        public void ConfirmModal(
            MessageBoxTester.Command command)
        {
            MessageBoxTester tester =
                new MessageBoxTester(
                    MainForm.ConfirmationDialogName);
            tester.SendCommand(command);
        }
    }
}

The ability to test modal dialogs programmatically is really valuable for non-regression testing of Windows Forms applications.