Hi all,
Can anyone help me writing the test class for my trigger.

trigger orderproduct on Order__c (after insert,after update) {
    Set<Id> opportunityIds = new Set<Id>();
    Set<Id> orderIds = new Set<Id>();
    List<Order__c> orderList = new List<Order__c>();
    Map<Id,Id> mapof = new Map<Id,Id>();
    for(Order__c o : Trigger.new)
    {
        if(o.Opportunity__c  != NULL)
        {
            opportunityIds.add(o.Opportunity__c );
            orderIds.add(o.Id);
            mapof.put(o.Opportunity__c ,o.Id);
        }
        
    }
    
    if(opportunityIds.size() > 0)
    {
        list<OpportunityLineItem__c> oppprodList = new list<OpportunityLineItem__c>([Select id,name,Product2Id__r.name,ListPrice__c,OpportunityId__c,Sales_Price__c,Quantity__c from OpportunityLineItem__c WHERE OpportunityId__c=:opportunityIds]);
        // Loop through orders
        List<OrderItem__c> orderItemsForInsert = new List<OrderItem__c>();
        for(OpportunityLineItem__c pd : oppprodList)
        {
            OrderItem__c oi = new OrderItem__c();
            oi.OrderId__c = mapof.get(pd.OpportunityId__c);
            oi.Name = pd.Product2Id__r.name;
            oi.ListPrice__c = pd.ListPrice__c;
            oi.Unit_Price__c = pd.Sales_Price__c;
            oi.Quantity__c = pd.Quantity__c;
            orderItemsForInsert.add(oi);
            
        }
        system.debug('sucess');                              
        if(orderItemsForInsert.size() > 0)
        {
             system.debug('orderItemsForInsert +' +orderItemsForInsert);  
            insert orderItemsForInsert;
        }
        
    }
}