code: public function start()
      {
          if(!$this->cli) {
              if (session_status() === PHP_SESSION_DISABLED) {
                  throw new InternalException('Sessions are disabled');
              }
  
              if (session_status() === PHP_SESSION_ACTIVE) {
                  throw new InternalException('Session already started.');
              }
  
              session_name($this->name); // set session name
              session_start();
  
              $this->id = session_id();
          } else {
              $this->clistore = array();
              $this->id = rand();
          }
      }
docs: Start session
  @codeCoverageIgnore