I get ID from java script, but test class is not work.

It is not error, but can not check something in the loop. How do I fix it.

Class

Public String OppID = ApexPages.currentPage().getParameters().get('Oppid');
List<Delivery__c> lsttmpDL = new List<Delivery__c>();

public PageReference SaveDelivery(){
       
        if(OppID != null){  //Pass
            for(Delivery__c DL : Deliverys){ /////////////////////////// Faild this test class not work. Can not check in the loop.
               Delivery__c tmpDL = New Delivery__c ();
               tmpDL.Ship_To_Account__c = DL.Ship_To_Account__c;
               tmpDL.Order_Taking__c = DL.Order_Taking__c ;
               tmpDL.Order_Reference__c = DL.Order_Reference__c ;
               tmpDL.Reference__c = DL.Reference__c;
               tmpDL.Est_Completed__c = DL.Est_Completed__c;
               tmpDL.PO_No__c = DL.PO_No__c;
               tmpDL.PO_Date__c = DL.PO_Date__c;
               tmpDL.Transfer_Date__c = DL.Transfer_Date__c;
               tmpDL.Discount_Order__c = DL.Discount_Order__c;
               tmpDL.Discount_Code_1__c = DL.Discount_Code_1__c;
               tmpDL.Remark__c = DL.Remark__c;
               lsttmpDL.Add(tmpDL);  
           }
           insert lsttmpDL ;
      }
}

 Test Class 

List<Delivery__c > objdelivery = new List<Delivery__c >();      
ApexPages.StandardSetController controller = new ApexPages.StandardSetController(objdelivery);
DeliveryPages clsTest = new DeliveryPages(controller);

Order_Taking__c OT = New Order_Taking__c();
OT.Periods_of_Order__c = 4;
insert OT;

ApexPages.currentPage().getParameters().put('OppID', OT.Id);

Delivery__c DL = New Delivery__c();
DL.Salesman_Code__c = '12344576';
DL.Order_Taking__c = OT.id;
Insert DL;

List<Delivery__c> lstDeliverys = new List<Delivery__c>();
lstDeliverys.Add(DL);

ApexPages.currentPage().getParameters().get('OppID');
clsTest.ShowDeliverys();

Best, Regards.