Add this to your Silverlight app to run tests

AddToApp.xaml.cs

// Add the following to your App.xaml.cs's 
// Application_Startup method.
var queryString = HtmlPage.Document.QueryString;
if (queryString.ContainsKey("test")) {
  var xap = new Uri(
    "eggs.xap", UriKind.Relative
  );
  WebClient wcXap = new WebClient();
  wcXap.OpenReadCompleted += 
    new OpenReadCompletedEventHandler(
      wcXap_OnOpenReadCompleted
    );
  wcXap.OpenReadAsync(xap);
}

AddToYourUsings.cs

// Add the following to your usings.
using System.Reflection;
using System.Windows.Browser;
using System.Windows.Resources;

AlsoAddToApp.xaml.cs

// Add this method to your App class. It is 
// called when eggs.xap is downloaded. It 
// defines where the tests are, and starts 
// running them.
private void 
wcXap_OnOpenReadCompleted
(object sender, OpenReadCompletedEventArgs e) {
  if ((e.Error == null) && 
      (e.Cancelled == false)){
    var xap = 
      new StreamResourceInfo(e.Result, null);
    Assembly asm = new AssemblyPart().Load(
      Application.GetResourceStream(
        xap, new Uri(
          "Eggs.dll", UriKind.Relative
        )
      ).Stream
    );
    asm.GetType("Eggs")
       .GetMethod("Start")
       .Invoke(null, new object[] {
         (object) new Uri(
           "http://localhost:35863/Sample.Tests.xap"
         ), 
         (object) xap
       }
    );
  }
}