code: func (m *Stub) Stop() error {
  	if m.server == nil {
  		return nil
  	}
  	m.server.Stop()
  	m.wg.Wait()
  	m.server = nil
  	close(m.stop) // This prevents re-starting the server.
  
  	return m.cleanup()
  }
docs: // Stop stops the gRPC server. Can be called without a prior Start
  // and more than once. Not safe to be called concurrently by different
  // goroutines!