In Advanced Apex Specialist Challenge 2
Challenge Not yet complete... here's what's wrong: Ensure that you call the correct method from orderTrigger.
My Trigger and helper class code I am pasting it here
trigger orderTrigger on Order (after update) {
 
    if(Trigger.new != null){   
            OrderHelper.AfterUpdate(Trigger.new,Trigger.old);       
    }
}
OrderHelper class
public class OrderHelper {
        /**
         * @name AfterUpdate
         * @description
         * @param List<Order> newList
         * @param List<Order> oldList
         * @return void
        **/
        public static void AfterUpdate(List<Order> newList, List<Order> oldList){
            Set<Id> activatedOrderIds = new Set<Id>();
            //Create list of OrderIds
            for ( Integer i=0; i<newList.size(); i++ ){
                if ((newList[i].Status == Constants.ACTIVATED_ORDER_STATUS && newList[i].ActivatedDate != null)
                    && oldList[i].Status == Constants.DRAFT_ORDER_STATUS){
                    activatedOrderIds.add(newList[i].Id);
                }
            }
            RollUpOrderItems(activatedOrderIds);
        }
        /**
         * @name RollUpOrderItems
         * @description Given a set of Activated Order ids, query the child Order Items and related Products to calculate Inventory levels
         * @param Set<Id> activatedOrderIds
         * @return void
        **/
        public static void RollUpOrderItems(Set<Id> activatedOrderIds){
            //ToDo: Declare a Map named "productMap" of Ids to Product2 records
            Map<Id, Product2> productMap = new Map<Id, Product2>();
            Set<Id> productIds = new Set<Id>();
            //ToDo: Loop through a query of OrderItems related to the activatedOrderIds
            List<OrderItem> items = [SELECT Id, Product2Id, Quantity
                                    FROM OrderItem
                                    WHERE OrderId In :activatedOrderIds];
            for(OrderItem oi : items) {
                //ToDo: Populate the map with the Id of the related Product2 as the key and Product2 record as the value
                productIds.add(oi.Product2Id);
            }
            productMap = new Map<Id, Product2>([SELECT Id, Quantity_Ordered__c FROM Product2 WHERE Id IN :productIds]);
            AggregateResult[] groupedResults = [SELECT Product2Id, SUM(Quantity) activatedQuantity
                                                 FROM OrderItem
                                                 WHERE Product2Id In :productMap.keySet() GROUP BY Product2Id];
            for (AggregateResult ar : groupedResults)  {
                productMap.get((String) ar.get('Product2Id')).Quantity_Ordered__c = Integer.valueOf(ar.get('activatedQuantity'));
            }
            //ToDo: Perform an update on the records in the productMap
            if(productMap!=null && productMap.size()>0){
                update productMap.values();
            }
        }
    }