How to unit test a static method using a fake object for the dependency?

Question

I've got my Fake object for HttpRequest ready (a wrapper and an interface)... since I don't need to call a constructor, how do I pass in the fake HttpRequest without breaking the interface of this method?

public static int ParseQueryInt(string key, int defaultValue)
{
   NameValueCollection nvc;
   if (HttpContext.Current.Request.QueryString["name"] != null)
   {
      //Parse strings.
   }
}

EDIT: Akselson's solution is the most creative and this proof of concept worked, much to my surprise, although I also used Skeet's solution as it look more likely to work in all situations.

public class Class1
{  
    [Test]
    public void Test()
    {
        HttpContext.Current = new HttpContext(
new HttpRequest("test.aspx", "http://test.com/test.aspx", "querystring=value"),
new HttpResponse(new StringWriter())
);
        Assert.AreEqual(HttpContext.Current.Request.QueryString["querystring"], "value");
    }
}

Answer 1

One option is introduce another overload:

public static int ParseQueryInt(string key, int defaultValue)
{
    return ParseQuery(key, defaultValue, HttpContext.Current.Request);
}

public static int ParseQueryInt(string key, int defaultValue, 
                                HttpRequest request)
{
   NameValueCollection nvc;
   if (request.QueryString["name"] != null)
   {
      //Parse strings.
   }
}

Then you reduce your "untestable" (or at least "hard to test") code to a simple redirection... you can test the heck out of the version which accepts a request.

Answer 2

You can set HttpContext.Current to your own instance:

HttpContext.Current = new HttpContext(
    new HttpRequest("test.aspx","http://test.com/test.aspx","querystring=value"),
    new HttpResponse(new StringWriter())
);

It might be useful if you don't want to change the method before you have it under test.