Returns whether the transaction is in a valid batch.

        Args:
            txn_id (str): The transaction header signature.

        Returns:
            (bool): True if the txn's batch is valid, False otherwise.

def _txn_is_in_valid_batch(self, txn_id):
        """Returns whether the transaction is in a valid batch.

        Args:
            txn_id (str): The transaction header signature.

        Returns:
            (bool): True if the txn's batch is valid, False otherwise.
        """

        batch = self._batches_by_txn_id[txn_id]

        # Return whether every transaction in the batch with a
        # transaction result is valid
        return all(
            self._txn_results[sig].is_valid
            for sig in set(self._txn_results).intersection(
                (txn.header_signature for txn in batch.transactions)))