UnitAura API is not working properly on WotLK Classic. The following call throws a LUA error UnitAura(“player”, “Power Word: Fortitude”, “Rank 8”, “HELPFUL”). This is intended to work at least on revision 3.3.5.12340, so it should be working on WotLK Live. There is a reference to this bug on wowpedia/wiki/Talk:API_UnitAura. UnitAura is only working when the arguments are “unit”, index, “filter”, ignoring the overload “unit”, “name”, “rank”, “filter”.
This breaks a lot of weakauras and addons, mostly rebuff weak auras, because you need to iterate over all the buffs/debuffs instead of searching for the specific buff/debuff of the unit. No idea if this is actually faster than iterating and breaking if aura is found tho.