I need to Test and Event
 

There is an event EVENT_LOOT_RECEIVED and there are a few different ways of defining it. The way that seems to be working is this
The Wiki is reporting it as (string receivedBy, string itemName, integer quantity, integer itemSound, integer lootType, bool self) which is one less parameter. I think tha the last parameter is important because I use it. Currently it's used in HarvestMap to see if the player looted the item. They can't both be right.

Can I call the event like, var1, var2, var3, var4, var5, var6, var7 = EVENT_LOOT_RECEIVED or do i need to register an event like "EVENT_MANAGER:RegisterForEvent("HarvestMap", EVENT_LOOT_RECEIVED, Harvest.OnLootReceived)" to that it will fire on auto loot and then try to decode those variables.

What is the best way to go about checking that?

EVENT_MANAGER:RegisterForEvent("HarvestMap", EVENT_LOOT_RECEIVED, Harvest.OnLootReceived) is the correct way to go about it because var1, var2, var3, var4, var5, var6, var7 = EVENT_LOOT_RECEIVED wouldn't do anything. Var1 would get assigned whatever random integer EVENT_LOOT_RECEIVED is and nothing else.

Best way to investigate events would be using zgoo imo. '/zgoo events' will bring up a frame that registers every event and you can examine their return values. You can block the events you don't want to see by clicking the X next to them, and expand to see return values with +. To avoid the hassle of Xing all events you don't want you could change the source code in Events.lua/Events:RegisterAllEvents() to only register the events you are concerned with.