Hi All ,
Getting assertion Failure for the below test class.
@isTest
Private class updateQtyTest{
    Static testMethod void UpdateQty(){
    
     Product2 Pd1=new Product2();
        Pd1.Name='Pd01';
        Pd1.Production_Location__c='SMT-TH';
        Pd1.SAP_Product_Nr__c='123';
        Pd1.Module_Source__c='bought';
        insert pd1;
        
        BillingDoc__c BD1=new BillingDoc__c();
            BD1.DocumentType__c='Test01';
            BD1.Name='001';
            BD1.Production_Location__c='SMT-TH';
            BD1.DocumentTypeCode__c='ZOR';
            BD1.DocumentDate__c=System.Today();
            BD1.FacturaDate__c=System.Today();
        insert BD1;

        
        BillingItem__c BI1= new BillingItem__c();
            BI1.Name='Sales Strategy Manager';
            BI1.ItemNo__c= '001';
            BI1.Quantity__c=23456;
            BI1.Units__c='PCE';
            BI1.UnitPrice__c=1000;
            BI1.PriceUnit__c=1;
            BI1.BillingDocumentId__c=BD1.ID;
            BI1.Product2__c=Pd1.ID;
            insert BI1;
       Test.startTest();
      BD1.DocumentTypeCode__c = 'ZR2';
      update BD1;
      
      test.stopTest();
      // Now check if it is giving desired results using system.assert
      // Total Quantity in Billing Document should be 0.
      List<BillingItem__c> BIList=[Select Name,Quantity__c,BillingDocumentId__c from BillingItem__c where id=:BI1.Id];
      System.assertEquals(0, BI1.Quantity__c);
      

}
}

Please Advise.

Thanks,
Silpi