Main.Controllers.ManageController.ChangeAvatar C# (CSharp) Method

        public ActionResult ChangeAvatar(string avatar) {

            if (ModelState.IsValid)
            {
                var UserID = User.Identity.GetUserId();
                AspNetUser user = db.AspNetUsers.Where(m => m.Id == UserID).FirstOrDefault();
                user.Avatar = avatar;
                db.Entry(user).State = EntityState.Modified;
                db.SaveChanges();
            }

            return RedirectToAction("index");
        }

 public void testChangeAvatar()
 {
     ManageController manageController = new ManageController();
     ActionResult changeAvatar = manageController.ChangeAvatar("HaveNeed");
 }