ASP.NET pages inside unit tests - AppDomainUnloadedException

Hello, I am experiencing a difficulty with running ASPX pages outside of IIS and even outside of HttpRuntime. These practices are not well documented, but I hope someone has already solved similar problem.

My goal is simple: Somehow create an instance of an ASPX page, run it and test what happens. Test values of some page's properties, properties of its controls and so on.

Here's where I came:

1. <div mce_keep="true">Create a new application domain (ApplicationHost.CreateApplicationHost).</div>
2. <div mce_keep="true">Compile the page and get its type (ClientBuildManager).</div>
3. <div mce_keep="true">Create a new HttpContext.</div>
4. <div mce_keep="true">Construct the page (Type.GetConstructor...).</div>
5. <div mce_keep="true">Then I can subscribe some events, if I want to test the page during its life-cycle.</div>
6. <div mce_keep="true">Run the page (page.ProcessRequest). Documentation says that this method is "not intended to be used directly from your code". However I didn't find any other way...</div>

And it works. This is the full code of a sample test fixture:

using System;
using System.Web;
using System.Web.Compilation;
using System.Web.Hosting;
using System.Web.UI;
using NUnit.Framework;
using NUnit.Framework.SyntaxHelpers;


namespace PageSharp.Incubator.Tests.Learning
{
    /// <summary>
    /// Test how could pages be programatically instantiated and executed.
    /// </summary>
    [TestFixture]
    public class PageLifeCycleLearningTest : MarshalByRefObject
    {
        private string _virtualDir = "/";
        private string _appDir;
        private PageLifeCycleLearningTest _host;


        public PageLifeCycleLearningTest()
        {
            _appDir = System.IO.Directory.GetCurrentDirectory().TrimEnd("bin".ToCharArray());
        }


        [TestFixtureSetUp]
        public void SetUp()
        {
            _host = (PageLifeCycleLearningTest)
                ApplicationHost.CreateApplicationHost(typeof(PageLifeCycleLearningTest), _virtualDir, _appDir);
        }


        [Test]
        public void TestSomeFact()
        {
            _host.TestSomeFact_Run();
        }


        private void TestSomeFact_Run()
        {
            var page = CreatePage("~/default.aspx", String.Empty);
            page.PreInit += new EventHandler(TestSomeFact_PreInit);
            page.ProcessRequest(HttpContext.Current);


            var ctl = (System.Web.UI.WebControls.Label) page.FindControl("ctl00$ContentPlaceHolder1$WebUserControl11$Label1");
            Assert.That(ctl.Text, Is.EqualTo("Hello World!"));
        }


        private void TestSomeFact_PreInit(object sender, EventArgs e)
        {
            var page = (Page)sender;
            var ctl = (System.Web.UI.WebControls.Label)page.FindControl("ctl00$ContentPlaceHolder1$WebUserControl11$Label1");
            Assert.That(ctl, Is.Null);
        }


        /// <summary>
        /// Compile and instantiate a page.
        /// </summary>
        /// <param name="virtualPath">Virtual path.</param>
        /// <param name="queryString">Query string.</param>
        /// <returns>Instance of the page.</returns>
        private Page CreatePage(string virtualPath, string queryString)
        {
            var cbm = new ClientBuildManager(_virtualDir, _appDir);
            var type = cbm.GetCompiledType(virtualPath);
            var writer = new System.IO.StringWriter();
            HttpContext.Current = new HttpContext(new SimpleWorkerRequest(virtualPath, queryString, writer));
            Page page = (Page)type.GetConstructor(new Type[] { }).Invoke(new object[] { });


            return page;
        }
    }
}

 There's just one remaining problem: A few moments after the test runs and passes, something throws System.AppDomainUnloadedException exception, with no stack trace available:

I can't find a way to avoid it. Probably I have to clean the AppDomain somehow, but how?