public void HeartBeatUserTest()
    {
      ITvCardContext ctx = new TvCardContext();

      IUser u1 = new User("u1", false, 1);
      DateTime oldHB = u1.HeartBeat;
      ctx.Add(u1);      

      ctx.HeartBeatUser(u1);

      Assert.AreNotEqual(u1.HeartBeat, oldHB, "heartbeat hasnt changed");
    }