code: def check_tx(self, raw_transaction):
          
  
          self.abort_if_abci_chain_is_not_synced()
  
          logger.debug('check_tx: %s', raw_transaction)
          transaction = decode_transaction(raw_transaction)
          if self.bigchaindb.is_valid_transaction(transaction):
              logger.debug('check_tx: VALID')
              return ResponseCheckTx(code=CodeTypeOk)
          else:
              logger.debug('check_tx: INVALID')
              return ResponseCheckTx(code=CodeTypeError)
docs: Validate the transaction before entry into
          the mempool.
  
          Args:
              raw_tx: a raw string (in bytes) transaction.