code: def _begin_validation(
          session: UpdateSession,
          loop: asyncio.AbstractEventLoop,
          downloaded_update_path: str,
          robot_name: str) -> asyncio.futures.Future:
      
      session.set_stage(Stages.VALIDATING)
  
      validation_future \
          = asyncio.ensure_future(loop.run_in_executor(
              None, validate_update,
              downloaded_update_path, session.set_progress))
  
      def validation_done(fut):
          exc = fut.exception()
          if exc:
              session.set_error(getattr(exc, 'short', str(type(exc))),
                                str(exc))
          else:
              rootfs_file, bootfs_file = fut.result()
              loop.call_soon_threadsafe(_begin_write,
                                        session,
                                        loop,
                                        rootfs_file,
                                        robot_name)
      validation_future.add_done_callback(validation_done)
      return validation_future
docs: Start the validation process.