ASP.NET Custom Control Adapter not firing

I am trying to write a simple ControlAdapter below is a very simplified case, but I still can't seem to get it to work. In my simplified case I just want to write something out before my control is rendered.

I defined my control adapter as such:

using System.Web.UI;
using System.Web.UI.WebControls.Adapters;

namespace Test.Web.Common.Controls.ControlAdapters {

  public class RadioBtnStyleAdapter : WebControlAdapter {


    protected override void BeginRender(HtmlTextWriter writer) {

      writer.WriteLine("<!--- CONTROL ADAPTER -->");
      writer.WriteLine("<div><b>TEST</b></div");

      base.BeginRender(writer);
    }
  }
}

I then added an App_Browsers folder under my Test.Web project.
I then added a default.browser file under App_Browsers

And my default.browsers looks like

<browsers>
  <browser id="Default">
    <controlAdapters>
      <adapter controlType="System.Web.UI.WebControls.RadioButton" adapterType="Test.Web.Common.Controls.ControlAdapters.RadioBtnStyleAdapter"></adapter>
    </controlAdapters>
  </browser>
</browsers>

It is my understanding that should be enough, and the framework should pick up the the adapter, however it never actually seems to fire.

Any suggestions about what I could be missing?

Update

I am able get it to work if I programmaticaly add the adapter on Page_Init like so

HttpContext.Current.Request.Browser.Adapters["System.Web.UI.WebControls.RadioButton"] = "Test.Web.Common.Controls.ControlAdapters.RadioBtnStyleAdapter";

But nothing I have read show this as a required step, so I am not convinced this is correct.

You need to change the id attribute of the browser element to refID as follows. The id attribute is used if you would like to give it a unique name, when mapping/identifying a particular browser, and refID is used when associating new capabilities (such as Control Adapters) with an existing browser definition. And that's exactly what you want to do.

<browsers>
  <browser refID="Default">
    <controlAdapters>
      <adapter controlType="System.Web.UI.WebControls.RadioButton" adapterType="Test.Web.Common.Controls.ControlAdapters.RadioBtnStyleAdapter"></adapter>
    </controlAdapters>
  </browser>
</browsers>