AxWebBrowser Control test fixture - InvalidActiveXStateException


I'm wondering if you can help me by getting the following test fixture to pass:

using System;
using System.Threading;
using AxSHDocVw;
using NUnit.Framework;
using Sidebet.Gui.Tools;

namespace Sidebet.Gui.TestFixtures
    public class InnerHtmlDownloaderTestFixture
        private bool _downloadComplete;
        private InnerHtmlDownloader downloader;
        private string url = "";

        private AxWebBrowser axWebBrowser1;

        public void SetUp()
            _downloadComplete = false;
            downloader = new InnerHtmlDownloader();
            axWebBrowser1 = new AxWebBrowser();

        public void TearDown()

        public void AxWebBrowserDownloadEvent()
            axWebBrowser1.DocumentComplete +=new DWebBrowserEvents2_DocumentCompleteEventHandler(axWebBrowser1_DocumentComplete);

                _downloadComplete = false;

            Assert.IsTrue(_downloadComplete, "Download event should have occured.");

        private void axWebBrowser1_DocumentComplete(object sender, DWebBrowserEvents2_DocumentCompleteEvent e)
            _downloadComplete = true;

When I run the test, I get the following exception caught by the try...catch block above"

"Exception of type 'System.Windows.Forms.AxHost+InvalidActiveXStateException' was thrown."

However, I have another application that this works fine with. I would like to write unit tests for my downloader class, but I cannot because I keep getting this error.

Any suggestions?
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Bob LearnedCommented:
That means that the ActiveX control needs to be hosted (sited) on a form, and cannot be instantiated the way that you are doing it.

sapbucketAuthor Commented:
That makes sense...

How would someone be able to test it using Test Driven Development? It is frustrating to be constrained by the type of project I am developing. My unit tests exist in a class library - whereas what I want to test is in a Windows Forms project.

I also tried creating a windows form with a AxWebBrowser in it. I then added a event handler that "wraps" the event produced by the AxWebBrowser. This had the added bonus of allowing me to pass further arguments too. I then created a testFixture class (this time in a windows form project) where I instance the form containing the AxWebBrowser, wired up a callback method to the wrappered event, then tried to have the windows form use the AxWebBrowser to download, and then I waited for the DocumentLoaded event to occur so that I could Assert that it had happened. This also did not work! I received the same error.

It would seem instancing and using a AxWebBrowser in any other place other than a windows form does not work. The windows form cannot be instanced from any other place - with the intent of using the AxWebBrowser - except for in another windows form (such as main()).

I have learned about another unit testing util called NUnitForms. Going to try it out this afternoon. However, if you know more about this type of thing please share!

Bob LearnedCommented:
Can you show me what you mean by instancing a form with a WebBrowser control on it?  Also, what .NET version do you have?

sapbucketAuthor Commented:
The solution is that you just can't do it. It creates a circular reference. There are many blogs that complain about this and talk about why you can't do it.

The future
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