feat(tests): BLOCKHASH recency window in state-test runner (#2943)

* feat: nethermind state test added

* fix: i was lINTING again

Author: felix314159

tests/frontier/opcodes/test_blockhash_state_test_recency.py

@@ -0,0 +1,151 @@
+"""
+State-test regression for the BLOCKHASH (0x40) opcode recency window.
+
+In a *state test*, nethermind returns a non-zero hash for
+``BLOCKHASH(0)`` even when block 0 lies far outside the recency window (256
+blocks pre-Prague, 8191 via EIP-2935 from Prague). eels (the reference),
+go-ethereum, besu, erigon, evmone and reth all correctly return 0.
+
+Root cause (nethermind, state-test only):
+``src/Nethermind/Ethereum.Test.Base/TestBlockhashProvider.cs`` implements::
+
+    number != 0 ? Keccak.Zero : Keccak.Compute(number.ToString())
+
+It performs no recency-window check, and the opcode handler
+``InstructionBlockHash`` (in ``EvmInstructions.Environment.cs``) delegates
+that check to the provider -- it only rejects ``number >= current``. So
+``BLOCKHASH(0)`` returns ``keccak256("0")`` regardless of how ancient block
+0 is. Nethermind's *production* ``BlockhashProvider`` does enforce the
+window, so this is a state-test tooling bug, not a mainnet consensus bug --
+but it makes nethermind diverge under differential state-test fuzzing.
+"""
+
+import pytest
+from execution_testing import (
+    Account,
+    Alloc,
+    Environment,
+    Hash,
+    Op,
+    StateTestFiller,
+    Storage,
+    Transaction,
+)
+
+# keccak256(b"0") -- the state-test convention hash for block 0 used by both
+# go-ethereum (vmTestBlockHash) and nethermind (TestBlockhashProvider). The
+# fuzzer sets env.previousHash to exactly this value so the in-window
+# block-0 hash agrees across clients.
+KECCAK_OF_BLOCK_0 = Hash(
+    0x044852B2A670ADE5407E78FB2863C51DE9FCB96542A07186FE3AEDA6BB8A116D
+)
+
+
+@pytest.mark.valid_from("Frontier")
+@pytest.mark.state_test_only
+@pytest.mark.parametrize(
+    "current_number",
+    [
+        pytest.param(0x101, id="just_past_256_window"),
+        pytest.param(0x2001, id="just_past_8191_window"),
+        pytest.param(0x100000, id="far_out_of_window"),
+        pytest.param(0xA63CCE, id="fuzzer_discovered_number"),
+    ],
+)
+def test_blockhash_zero_out_of_window(
+    state_test: StateTestFiller,
+    pre: Alloc,
+    current_number: int,
+) -> None:
+    """
+    BLOCKHASH(0) must be 0 when block 0 is outside the recency window.
+
+    At ``current_number`` well past the window, block 0 is ancient, so every
+    spec-conformant client returns 0. Nethermind's state-test runner instead
+    returns ``keccak256("0")`` because ``TestBlockhashProvider`` skips the
+    window check, which is the bug this test guards against.
+
+    Marked ``state_test_only``: the bug lives solely in the state-test code
+    path (the production blockhash provider enforces the window), and a state
+    test with such a high ``env.number`` cannot be converted into a real
+    blockchain-test fixture (no genesis chain up to that height).
+    """
+    storage = Storage()
+    contract = pre.deploy_contract(
+        code=(
+            # slot 0: the raw hash -- must be zero
+            Op.SSTORE(
+                storage.store_next(0, "blockhash_0_value"),
+                Op.BLOCKHASH(0),
+            )
+            # slot 1: ISZERO of the hash -- must be 1 (written, so the
+            # divergence lands in a non-default slot too)
+            + Op.SSTORE(
+                storage.store_next(1, "blockhash_0_is_zero"),
+                Op.ISZERO(Op.BLOCKHASH(0)),
+            )
+        )
+    )
+    sender = pre.fund_eoa()
+
+    tx = Transaction(
+        sender=sender,
+        to=contract,
+        gas_limit=200_000,
+        protected=False,  # legacy tx so it fills on pre-EIP-155 forks too
+    )
+
+    state_test(
+        env=Environment(number=current_number),
+        pre=pre,
+        post={contract: Account(storage=storage)},
+        tx=tx,
+    )
+
+
+@pytest.mark.valid_from("Frontier")
+@pytest.mark.valid_until("Cancun")
+@pytest.mark.state_test_only
+def test_blockhash_zero_in_window_control(
+    state_test: StateTestFiller,
+    pre: Alloc,
+) -> None:
+    """
+    In-window control: BLOCKHASH(0) returns the block-0 hash at block 1.
+
+    This is the positive counterpart to the out-of-window test. With block 0
+    inside the recency window (current block == 1) and ``previousHash`` set
+    to the state-test convention value ``keccak256("0")``, all clients --
+    including nethermind -- agree on the result, pinning the window boundary.
+
+    Restricted to <= Cancun because EIP-2935 (Prague+) serves BLOCKHASH from
+    the history storage contract, which is not pre-populated in a bare state
+    test.
+    Marked ``state_test_only``: the asserted non-zero hash would not match the
+    real genesis hash of a derived blockchain-test fixture.
+    """
+    storage = Storage()
+    contract = pre.deploy_contract(
+        code=Op.SSTORE(
+            storage.store_next(KECCAK_OF_BLOCK_0, "blockhash_0_value"),
+            Op.BLOCKHASH(0),
+        )
+    )
+    sender = pre.fund_eoa()
+
+    tx = Transaction(
+        sender=sender,
+        to=contract,
+        gas_limit=200_000,
+        protected=False,  # legacy tx so it fills on pre-EIP-155 forks too
+    )
+
+    state_test(
+        env=Environment(
+            number=1,
+            block_hashes={0: KECCAK_OF_BLOCK_0},
+        ),
+        pre=pre,
+        post={contract: Account(storage=storage)},
+        tx=tx,
+    )