[{"_id":1,"religion":"south","tested":true,"fruit":"apple","created_at":123333444},{"_id":2,"religion":"south","tested":true,"fruit":"orange","created_at":2211123333},{"_id":5,"religion":"south","tested":true,"fruit":"orange","created_at":2211123333},{"_id":3,"religion":"north","tested":false,"fruit":"apple","created_at":223444433},{"_id":4,"religion":"north","tested":true,"fruit":"orange","created_at":234567876}]

db.collection.aggregate([{"$group":{"_id":null,"fruit":{"$addToSet":{"$cond":[{"$and":[{"$eq":["$religion","south"]},{"$eq":["$tested",true]}]},"$fruit","$$REMOVE"]}}}},{"$project":{fruit:1,_id:0}}])