trigger ProductRevenue on ProductStore__c (after update) {

    List<Revenue__C> newOpps = new List<Revenue__C>();

  for (ProductStore__c prodobj : Trigger.new) {

      Revenue__C revobj = new Revenue__c();
      if(prodobj.QuantitySold__c > 1)
      {
      revobj.Transaction__C = prodobj.QuantitySold__c + ' ' + prodobj.Name__c + 's' + ' ' + 'sold';
      }

      else
      {
       revobj.Transaction__C = prodobj.QuantitySold__c + ' ' + prodobj.Name__c + ' ' + 'sold';
      }

      revobj.Revenue__c = (prodobj.QuantitySold__c)*(prodobj.Price__C);
      revobj.DateTime__C = datetime.now();
      revobj.ProductType__C = prodobj.Name__c;
      revobj.QuantitySold__C = prodobj.QuantitySold__c;



      newOpps.add(revobj);

  }
insert newOpps;

}

@isTest
private class TestProductRevenue {

   static testMethod void Testing()

   {

       List<ProductStore__c> newlist = new List<ProductStore__c>();
       ProductStore__c obj = new ProductStore__C ();
       obj = [SELECT ProductStore__c.QuantitySold__C FROM ProductStore__c WHERE ProductStore__c.Name = 'AC'];
       obj.QuantitySold__C = 2;
       newlist.add(obj);

       Test.startTest();
       update newlist;
       Test.stopTest();

   }

}