NUnit Test cases for ASp.net Webservices with HTTPContext

I have a case where i have to test Webservices methods which do not have HTTPContext as method parameters, but uses HTTPContext whcih comes from the browser inside the method.It is something like below:

[WebMethod()]

{

string result = String.Empty;

try

{

result = new AnotherClass().anotherMethod(classB.UserName(Context));

}

catch (Exception e)

{

throw new WebServiceException(e);

}

return result;

}