JS:
var payload = new FormData();
payload.append('TestTitle', $('#TestTitle').text());
payload.append('TestId', $('#TestId').val());
payload.append('TestGuid', $('#TestGuid').val());

var xhr = new XMLHttpRequest();
xhr.addEventListener('readystatechange', onStateChange);
xhr.open('POST', '/test/savetest?rand=' + Math.random());
xhr.send(payload);

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C#:
[HttpPost]
public ActionResult SaveTest(TestViewModel model)
{
   if (ModelState.IsValid)
   {
       //do stuff
   }
   return new JsonResult() { Data = new { Success = false }, JsonRequestBehavior = JsonRequestBehavior.AllowGet };
}