How to mock batch commit of transactions in Python

import json
from datetime import datetime, timezone

class TransactionBatch:
    def __init__(self):
        self.pending = []
        self.committed = []
        self._log = []

    def add(self, operation):
        self.pending.append(operation)

    def commit(self):
        if not self.pending:
            return False
        batch_id = f"batch_{len(self.committed) + 1}_{int(datetime.now(timezone.utc).timestamp())}"
        self.committed.append({
            "id": batch_id,
            "operations": self.pending[:],
            "committed_at": datetime.now(timezone.utc).isoformat()
        })
        self._log.append(f"Committed {len(self.pending)} ops as {batch_id}")
        self.pending = []
        return True

    def rollback(self):
        rolled_back = self.pending[:]
        self.pending = []
        self._log.append(f"Rolled back {len(rolled_back)} ops")
        return rolled_back

    def summary(self):
        return {
            "pending": len(self.pending),
            "committed_batches": len(self.committed),
            "total_committed_ops": sum(len(b["operations"]) for b in self.committed)
        }


if __name__ == "__main__":
    batch = TransactionBatch()
    batch.add({"type": "INSERT", "table": "users", "row": {"id": 1, "name": "Alice"}})
    batch.add({"type": "UPDATE", "table": "users", "row": {"id": 1, "name": "Alice A."}})
    batch.add({"type": "INSERT", "table": "orders", "row": {"id": 100, "user_id": 1}})

    print("Before commit:", batch.summary())
    ok = batch.commit()
    print("Commit success:", ok)
    print("After commit:", batch.summary())
    print("First committed batch id:", batch.committed[0]["id"])
    print("Log:", batch._log)