How can I prepare an argument of type HttpContext for a method?

I am trying test a method. The method takes in a single argument, which belongs to the class HttpContext in NET Framework Class Library. So I guess I need to prepare an object of HttpContext.

All that the method needs from the argument, say context, are

• context.Request.QueryString
• context.Request.Headers

Here are my thoughts and questions

1. To learn how to use HttpContext, I click going to definition in Visual Studio, I found that the class has a constructor

       public HttpContext(HttpRequest request, HttpResponse response);
   
   

   so I need to provide its two arguments, in order to create a object of the class.

   To provide an object of HttpRequest, I found its constructor

   //
   // Summary:
   //     Initializes an System.Web.HttpRequest object.
   //
   // Parameters:
   //   filename:
   //     The name of the file associated with the request.
   //
   //   url:
   //     The information regarding the URL of the current request.
   //
   //   queryString:
   //     The entire query string sent with the request (everything after the'?').
   public HttpRequest(string filename, string url, string queryString);
   
   

   • What does filename mean?

   • Which is url, the full url containing the query strings, or just the part before ??

2. After I can create an object of HttpContext, do I need to call some method to parse the url and query strings to obtain

   • context.Request.QueryString
   • context.Request.Headers

   or the HttpContext will implicitly do the work without me explicitly calling any method?

Thanks.