func (s *PresenceSuite) TestExpiry(c *C) {
	w := presence.NewWatcher(s.presence)
	p := presence.NewPinger(s.presence, "a")
	defer w.Stop()
	defer p.Stop()

	ch := make(chan presence.Change)
	w.Watch("a", ch)
	assertChange(c, ch, presence.Change{"a", false})

	c.Assert(p.Start(), IsNil)
	w.StartSync()
	assertChange(c, ch, presence.Change{"a", true})

	// Still alive in previous slot.
	presence.FakeTimeSlot(1)
	w.StartSync()
	assertNoChange(c, ch)

	// Two last slots are empty.
	presence.FakeTimeSlot(2)
	w.StartSync()
	assertChange(c, ch, presence.Change{"a", false})

	// Already dead so killing isn't noticed.
	p.Kill()
	w.StartSync()
	assertNoChange(c, ch)
}
func (s *PresenceSuite) SetUpTest(c *C) {
	s.LoggingSuite.SetUpTest(c)
	s.MgoSuite.SetUpTest(c)

	db := s.MgoSuite.Session.DB("presence")
	s.presence = db.C("presence")
	s.pings = db.C("presence.pings")

	presence.FakeTimeSlot(0)
}