test_bal_intra_tx_round_trip_after_prior_tx_write()

Documentation for tests/amsterdam/eip7928_block_level_access_lists/test_block_access_lists_cross_index.py::test_bal_intra_tx_round_trip_after_prior_tx_write@87aba1a3.

Generate fixtures for these test cases for Amsterdam with:

fill -v tests/amsterdam/eip7928_block_level_access_lists/test_block_access_lists_cross_index.py::test_bal_intra_tx_round_trip_after_prior_tx_write --fork Amsterdam

Verify a per-tx no-op SSTORE round-trip is not recorded as a storage change when an earlier tx in the same block wrote the slot.

Per EIP-7928 §Storage, a write is compared against "the storage value as of immediately before the current block_access_index (i.e., the cumulative state from all prior indices, falling back to the pre-block state)", and "a no-op write MUST NOT remove storage_changes entries from earlier indices for the same slot".

Both txs call the same contract whose runtime SSTOREs 0xff then 0x42 to slot 1. Tx 1 changes slot 1 from 0 to 0x42 (real change). Tx 1's write becomes tx 2's baseline, so tx 2's 0x42 -> 0xff -> 0x42 nets to a no-op and only tx 1 appears in storage_changes (with tx 1's entry left intact).

Source code in tests/amsterdam/eip7928_block_level_access_lists/test_block_access_lists_cross_index.py

def test_bal_intra_tx_round_trip_after_prior_tx_write(
    pre: Alloc,
    blockchain_test: BlockchainTestFiller,
) -> None:
    """
    Verify a per-tx no-op SSTORE round-trip is not recorded as a storage
    change when an earlier tx in the same block wrote the slot.

    Per EIP-7928 §Storage, a write is compared against "the storage value
    as of immediately before the current `block_access_index` (i.e., the
    cumulative state from all prior indices, falling back to the pre-block
    state)", and "a no-op write MUST NOT remove `storage_changes` entries
    from earlier indices for the same slot".

    Both txs call the same contract whose runtime SSTOREs 0xff then 0x42
    to slot 1. Tx 1 changes slot 1 from 0 to 0x42 (real change). Tx 1's
    write becomes tx 2's baseline, so tx 2's 0x42 -> 0xff -> 0x42 nets to
    a no-op and only tx 1 appears in `storage_changes` (with tx 1's entry
    left intact).
    """
    # Runtime: write 0xff to slot 1, then write 0x42 to slot 1, STOP.
    # The two SSTOREs hit the journal at every call, but the net effect
    # on the slot is `pre_value -> 0x42` — a no-op when pre_value == 0x42.
    contract_code = Bytecode(Op.SSTORE(1, 0xFF) + Op.SSTORE(1, 0x42) + Op.STOP)
    contract = pre.deploy_contract(code=contract_code)

    sender_a = pre.fund_eoa()
    sender_b = pre.fund_eoa()

    # Both txs go into the same block; tx 1 makes the real 0 -> 0x42
    # change, tx 2 starts from 0x42 and ends at 0x42 (per-tx no-op).
    tx_1 = Transaction(sender=sender_a, to=contract)
    tx_2 = Transaction(sender=sender_b, to=contract)

    expected_block_access_list = BlockAccessListExpectation(
        account_expectations={
            contract: BalAccountExpectation(
                # Only tx 1's real change appears. Tx 2's same-value
                # round-trip MUST be classified as a read for tx 2.
                storage_changes=[
                    BalStorageSlot(
                        slot=1,
                        slot_changes=[
                            BalStorageChange(
                                block_access_index=1, post_value=0x42
                            ),
                        ],
                    ),
                ],
                # `storage_changes` is only verified as a sub-sequence
                # at fill time, so this additional check guards against a
                # reference regression that emits tx 2's no-op as a
                # spurious index-2 change.
                absent_values=BalAccountAbsentValues(
                    storage_changes=[
                        BalStorageSlot(
                            slot=1,
                            slot_changes=[
                                BalStorageChange(
                                    block_access_index=2, post_value=0x42
                                ),
                            ],
                        ),
                    ],
                ),
            ),
            sender_a: BalAccountExpectation(
                nonce_changes=[
                    BalNonceChange(block_access_index=1, post_nonce=1),
                ],
            ),
            sender_b: BalAccountExpectation(
                nonce_changes=[
                    BalNonceChange(block_access_index=2, post_nonce=1),
                ],
            ),
        }
    )

    blockchain_test(
        pre=pre,
        blocks=[
            Block(
                txs=[tx_1, tx_2],
                expected_block_access_list=expected_block_access_list,
            ),
        ],
        post={contract: Account(storage={1: 0x42})},
    )

Parametrized Test Cases

This test generates 1 parametrized test case across 1 fork.