How To Make HttpContext Available To Be Used By My Unit Tests

I want to write a unit test which tests the function of a class called UploadedFile. The problem I face is this class' static constructor uses HttpContext.Current property and because I am running my unit test from a class library I do not have an HttpContext at the testing time.

Look at my static constructor:

static UploadedFile()
{
if (HttpContext.Current == null)[code]....

What should I do in my testing environment so that HttpContext.Current won't be null and I can successfully set this:

HttpServerUtility server = HttpContext.Current.Server;