code: func (s *SupportImpl) GetTxSimulator(ledgername string, txid string) (ledger.TxSimulator, error) {
  	lgr := s.Peer.GetLedger(ledgername)
  	if lgr == nil {
  		return nil, errors.Errorf("Channel does not exist: %s", ledgername)
  	}
  	return lgr.NewTxSimulator(txid)
  }
docs: // GetTxSimulator returns the transaction simulator for the specified ledger
  // a client may obtain more than one such simulator; they are made unique
  // by way of the supplied txid