function OnEnterCombat(Unit, event, pAttacker)
    Unit:SendChatMessage(12, 0, "Started fighting", 0)
    Unit:RegisterEvent("OnEnterTrigger", 1000, 1);
end

function OnEnterTrigger(Unit, event)
    Unit:SendChatMessage(12, 0, "Triggered OnEnterTrigger, registered with Unit:RegisterEvent", 0)
end

RegisterUnitEvent(5992, 1, OnEnterCombat)