feat: Validate t8n BAL does not have duplicate entries for the same tx_index

Author: fselmo

src/ethereum_test_types/block_access_list/__init__.py

@@ -360,6 +360,15 @@ def _validate_bal_ordering(bal: "BlockAccessList") -> None:
                                 f"Account {account.address}, Slot {slot_change.slot}: "
                                 f"tx_indices not in ascending order. Got: {tx_indices}"
                             )
+                        # Check for duplicate indices - each slot change must have a
+                        # unique tx_index
+                        if len(tx_indices) != len(set(tx_indices)):
+                            duplicates = [idx for idx in tx_indices if tx_indices.count(idx) > 1]
+                            raise BlockAccessListValidationError(
+                                f"Account {account.address}, Slot {slot_change.slot}: "
+                                f"has duplicate tx_indices. Got: {tx_indices}, "
+                                f"Duplicates: {list(set(duplicates))}"
+                            )
 
             # Check storage reads are in lexicographic order
             if account.storage_reads:
@@ -385,6 +394,12 @@ def _validate_bal_ordering(bal: "BlockAccessList") -> None:
                             f"Account {account.address}: {field_name} tx_indices "
                             f"not in ascending order. Got: {tx_indices}"
                         )
+                    if len(tx_indices) != len(set(tx_indices)):
+                        duplicates = [idx for idx in tx_indices if tx_indices.count(idx) > 1]
+                        raise BlockAccessListValidationError(
+                            f"Account {account.address}: {field_name} has duplicate tx_indices. "
+                            f"Got: {tx_indices}, Duplicates: {list(set(duplicates))}"
+                        )
 
     def _compare_account_expectations(
         self, expected: BalAccountExpectation, actual: BalAccountChange

src/ethereum_test_types/tests/test_block_access_lists.py

@@ -341,6 +341,78 @@ def test_actual_bal_tx_indices_ordering(field_name):
         expectation.verify_against(actual_bal)
 
 
+@pytest.mark.parametrize(
+    "field_name",
+    ["nonce_changes", "balance_changes", "code_changes"],
+)
+def test_actual_bal_duplicate_tx_indices(field_name):
+    """Test that actual BAL must not have duplicate tx indices in change lists."""
+    addr = Address(0xA)
+
+    # Duplicate tx_index=1
+    changes = []
+    if field_name == "nonce_changes":
+        changes = [
+            BalNonceChange(tx_index=1, post_nonce=1),
+            BalNonceChange(tx_index=1, post_nonce=2),  # duplicate tx_index
+            BalNonceChange(tx_index=2, post_nonce=3),
+        ]
+    elif field_name == "balance_changes":
+        changes = [
+            BalBalanceChange(tx_index=1, post_balance=100),
+            BalBalanceChange(tx_index=1, post_balance=200),  # duplicate tx_index
+            BalBalanceChange(tx_index=2, post_balance=300),
+        ]
+    elif field_name == "code_changes":
+        changes = [
+            BalCodeChange(tx_index=1, new_code=b"code1"),
+            BalCodeChange(tx_index=1, new_code=b""),  # duplicate tx_index
+            BalCodeChange(tx_index=2, new_code=b"code2"),
+        ]
+
+    actual_bal = BlockAccessList([BalAccountChange(address=addr, **{field_name: changes})])
+
+    expectation = BlockAccessListExpectation(account_expectations={})
+
+    with pytest.raises(
+        BlockAccessListValidationError,
+        match=f"{field_name} has duplicate tx_indices.*Duplicates: \\[1\\]",
+    ):
+        expectation.verify_against(actual_bal)
+
+
+def test_actual_bal_storage_duplicate_tx_indices():
+    """Test that storage changes must not have duplicate tx indices within same slot."""
+    addr = Address(0xA)
+
+    # Create storage changes with duplicate tx_index within the same slot
+    actual_bal = BlockAccessList(
+        [
+            BalAccountChange(
+                address=addr,
+                storage_changes=[
+                    BalStorageSlot(
+                        slot=0x01,
+                        slot_changes=[
+                            BalStorageChange(tx_index=1, post_value=0x100),
+                            BalStorageChange(tx_index=1, post_value=0x200),  # duplicate tx_index
+                            BalStorageChange(tx_index=2, post_value=0x300),
+                        ],
+                    )
+                ],
+            )
+        ]
+    )
+
+    expectation = BlockAccessListExpectation(account_expectations={})
+
+    with pytest.raises(
+        BlockAccessListValidationError,
+        match="Slot 0x.*1: has duplicate tx_indices.*Duplicates: \\[1\\]",
+    ):
+        expectation.verify_against(actual_bal)
+
+
 def test_expected_addresses_auto_sorted():
     """
     Test that expected addresses are automatically sorted before comparison.