code: private function spawnRpqInstance($withTest = false)
      {
          $command = sprintf(
              '%s queue -c %s',
              $_SERVER["SCRIPT_FILENAME"],
              $this->args['configFile']
          );
  
          if ($withTest) {
              $command = "exec {$command} -t";
          } else {
              $command = "exec {$command} > /dev/null 2>&1 &";
          }
  
          // Spawns a detached process
          $process = new Process($command);
          $process->disableOutput();
          $process->start();
  
          if ($withTest) {
              $process->wait();
              $code = $process->getExitCode();
  
              return $code === 0;
          }
  
          return yield $process->getPid();
      }
docs: Executes a self test by running `./rpq queue -t -c <config_file>.
  This method is blocking until the self test finishes, and the
  self test will be run within a separate process space.
  
  @return mixed