@Test
     public void test() {
         Attachment fetchedAttachment = (Attachment) MongoHelper.fetch(attachment, "attachments");
         if(fetchedAttachment == null)
             TestHelper.failed("attachment not found");
         
         fetchedAttachment.setFileName("changed.txt");
         if(!MongoHelper.save(fetchedAttachment, "attachments")){
             TestHelper.failed("FileName update failed");
         }
       
         Attachment updatedAttachment = (Attachment) MongoHelper.fetch(fetchedAttachment, "attachments");

         TestHelper.asserting(fetchedAttachment.getFileName().equals(updatedAttachment.getFileName()));
      
         System.out.println("updated Attachment id: " + updatedAttachment.getId());
         
         TestHelper.passed();
     }