c# - WebApi Unit Test HttpContextHelper with Mock -

i have method i'm trying mock (moq) unit testing i'm having difficulty props read , mocking fails sealed class. method hung off controller , have infrastructure in place.

first here method i'm trying test.

public carresponse(common.models.car car) {     string currentaccepttype = httpcontexthelper.current.request.headers["accept"];      ....removed brevity.....  } 

i have tried inject instantiated object , work headers read can't see how set headers want??

httprequest cv = new httprequest(null, "http://localhost:24244", "/cars/_services/addnewpickup"); //so far when want add headers every property read only. cv.headers.add("qewr", "adsf"); //this fails. 

msdn

ultimately using part of larger fake "session" testing.

httpcontext.current = new httpcontext(cv, new httpresponse(null)); 

mocking of httprequest fails sealed class.

so i'm kinda stumped on how test unit of code.