I am receiving DML error "cannot_insert_update_activate_entity, CreateAssetonClosedWon Line 43 of testCreateAssetonClosedWon execution of BeforeUpdate" I thought the record was locked but I get the same error attempting to use AfterUpdate as well.

Test Class

@isTest 

private class testCreateAssetonClosedWon {
    
    static testMethod void testCreateAssetonClosedWon(){
    	System.debug('Alerting on --------> Starting the TestCreateAssetonClosedWon ');
        List<OpportunityLineItem> insertOl = new List<OpportunityLineItem>{};
        Account a = [select Id from Account limit 1];
        System.debug('Alerting on --------> Account a -'+a);
        PricebookEntry pbID = [select Id from PricebookEntry where isactive = true limit 1];
        System.debug('Alerting on --------> PricebookEntry a -'+pbID);
        List<Opportunity> opp = new List<Opportunity>{};
        
        for(Integer i=0;i<200;i++){
        	Opportunity o = new Opportunity();
        	o.AccountId = a.Id;
        	o.Name = 'test';
        	o.StageName = '0-Prospecting';
        	o.CloseDate = date.today();
        	opp.add(o);
       
        }
        	insert opp;
        	System.debug('Alerting on --------> Opportunity opp insert');
        	
        	for(Integer j=0;j<opp.size();j++){
        		OpportunityLineItem ol = new OpportunityLineItem();

			      	ol.OpportunityId = opp[j].Id;
      				ol.Quantity = 1;
       				ol.UnitPrice = 2.00;
	        		ol.PricebookEntryId = pbId.Id;
	        		insertOl.add(ol); 
        	}
        		insert insertOl;
        		System.debug('Alerting on --------> LineItem ol insert '+insertOl);
        	
        	for(Integer ou=0;ou <opp.size();ou++){
        		opp[ou].StageName = '8-Closed';
        		System.debug('Alerting on --------> Opportunity Stagel opp '+opp[ou].StageName+' - '+opp[ou].ID);
        	}
        	Test.startTest();
        	update opp;
        	Test.stopTest();

        
        //o.AccountId = a.Id;
        //o.Name = 'test';
        //o.StageName = '0-Prospecting';
        //o.CloseDate = date.today();
        //insert o;
        
//        ol.OpportunityId = o.Id;
//        ol.Quantity = 1;
//        ol.UnitPrice = 2.00;
//        ol.PricebookEntryId = pbId.Id;
        
//        insert ol;
        
//        o.StageName= '8-Closed';
//        update o;
        
       // delete ol;
        //delete o;
        
        
        
    }
    
    
}

Trigger:

trigger CreateAssetonClosedWon on Opportunity (after update) {
     Set<id> opSet = new Set<id>(); 
     for(Opportunity o:Trigger.new)
     	opSet.add(o.id); 
     	System.debug('Alerting on --------> Starting the CreateAssetonClosedWon Trigger');
     	Map<id, OpportunityLineItem> owners = new Map<id, OpportunityLineItem>([Select UnitPrice, Quantity, PricebookEntry.Product2Id, PricebookEntry.Product2.Name, Description, Converted_to_Asset__c  
                                      From OpportunityLineItem 
                                      where OpportunityId in :opSet  and Converted_to_Asset__c = false]);     	
     
 
     for(Opportunity o:Trigger.new)
      //if(o.isWon == true && o.HasOpportunityLineItem == true){
      if(Trigger.isUpdate){
      	if(o.stageName == '8-Closed' && o.HasOpportunityLineItem == true){
         Asset[] ast = new Asset[]{};
         Asset a = new Asset();
     //    for(OpportunityLineItem ol: OLI){
            a = new Asset();
            a.AccountId = o.AccountId;
            a.Product2Id = owners.get(o.Id).PricebookEntry.Product2Id; 
            a.Quantity = owners.get(o.Id).Quantity;
            a.Price =  owners.get(o.Id).UnitPrice;
            a.PurchaseDate = o.CloseDate;
            a.Status = 'Purchased';
            a.Description = owners.get(o.Id).Description;
            a.Name = owners.get(o.Id).PricebookEntry.Product2.Name;
            ast.add(a);
            owners.get(o.Id).Converted_to_Asset__c = true;
     //  }
      update owners.get(o.id); 
      insert ast;
     	}
      }
	}