code: func (s *Simulation) StopRandomNodes(count int) (ids []enode.ID, err error) {
  	ids = make([]enode.ID, 0, count)
  	for i := 0; i < count; i++ {
  		n := s.Net.GetRandomUpNode()
  		if n == nil {
  			return nil, ErrNodeNotFound
  		}
  		err = s.Net.Stop(n.ID())
  		if err != nil {
  			return nil, err
  		}
  		ids = append(ids, n.ID())
  	}
  	return ids, nil
  }
docs: // StopRandomNodes stops random nodes.