fix(test-tests): Use ZeroPaddedHexNumber instead of HexNumber for BALs

packages/testing/src/execution_testing/test_types/block_access_list/account_changes.py

@@ -13,8 +13,8 @@
     Address,
     Bytes,
     CamelModel,
-    HexNumber,
     RLPSerializable,
+    ZeroPaddedHexNumber,
 )
 
 
@@ -23,11 +23,11 @@ class BalNonceChange(CamelModel, RLPSerializable):
 
     model_config = CamelModel.model_config | {"extra": "forbid"}
 
-    block_access_index: HexNumber = Field(
-        HexNumber(1),
+    block_access_index: ZeroPaddedHexNumber = Field(
+        ZeroPaddedHexNumber(1),
         description="Transaction index where the change occurred",
     )
-    post_nonce: HexNumber = Field(
+    post_nonce: ZeroPaddedHexNumber = Field(
         ..., description="Nonce value after the transaction"
     )
 
@@ -39,11 +39,11 @@ class BalBalanceChange(CamelModel, RLPSerializable):
 
     model_config = CamelModel.model_config | {"extra": "forbid"}
 
-    block_access_index: HexNumber = Field(
-        HexNumber(1),
+    block_access_index: ZeroPaddedHexNumber = Field(
+        ZeroPaddedHexNumber(1),
         description="Transaction index where the change occurred",
     )
-    post_balance: HexNumber = Field(
+    post_balance: ZeroPaddedHexNumber = Field(
         ..., description="Balance after the transaction"
     )
 
@@ -55,8 +55,8 @@ class BalCodeChange(CamelModel, RLPSerializable):
 
     model_config = CamelModel.model_config | {"extra": "forbid"}
 
-    block_access_index: HexNumber = Field(
-        HexNumber(1),
+    block_access_index: ZeroPaddedHexNumber = Field(
+        ZeroPaddedHexNumber(1),
         description="Transaction index where the change occurred",
     )
     new_code: Bytes = Field(..., description="New code bytes")
@@ -69,11 +69,11 @@ class BalStorageChange(CamelModel, RLPSerializable):
 
     model_config = CamelModel.model_config | {"extra": "forbid"}
 
-    block_access_index: HexNumber = Field(
-        HexNumber(1),
+    block_access_index: ZeroPaddedHexNumber = Field(
+        ZeroPaddedHexNumber(1),
         description="Transaction index where the change occurred",
     )
-    post_value: HexNumber = Field(
+    post_value: ZeroPaddedHexNumber = Field(
         ..., description="Value after the transaction"
     )
 
@@ -85,7 +85,7 @@ class BalStorageSlot(CamelModel, RLPSerializable):
 
     model_config = CamelModel.model_config | {"extra": "forbid"}
 
-    slot: HexNumber = Field(..., description="Storage slot key")
+    slot: ZeroPaddedHexNumber = Field(..., description="Storage slot key")
     slot_changes: List[BalStorageChange] = Field(
         default_factory=list, description="List of changes to this slot"
     )
@@ -111,7 +111,7 @@ class BalAccountChange(CamelModel, RLPSerializable):
     storage_changes: List[BalStorageSlot] = Field(
         default_factory=list, description="List of storage changes"
     )
-    storage_reads: List[HexNumber] = Field(
+    storage_reads: List[ZeroPaddedHexNumber] = Field(
         default_factory=list,
         description="List of storage slots that were read",
     )

packages/testing/src/execution_testing/test_types/block_access_list/modifiers.py

@@ -8,7 +8,10 @@
 
 from typing import Any, Callable, List, Optional
 
-from execution_testing.base_types import Address, HexNumber
+from execution_testing.base_types import (
+    Address,
+    ZeroPaddedHexNumber,
+)
 
 from .. import BalCodeChange
 from . import (
@@ -257,31 +260,43 @@ def transform(bal: BlockAccessList) -> BlockAccessList:
                 for nonce_change in new_account.nonce_changes:
                     if nonce_change.block_access_index == tx1:
                         nonce_indices[tx1] = True
-                        nonce_change.block_access_index = HexNumber(tx2)
+                        nonce_change.block_access_index = ZeroPaddedHexNumber(
+                            tx2
+                        )
                     elif nonce_change.block_access_index == tx2:
                         nonce_indices[tx2] = True
-                        nonce_change.block_access_index = HexNumber(tx1)
+                        nonce_change.block_access_index = ZeroPaddedHexNumber(
+                            tx1
+                        )
 
             # Swap in balance changes
             if new_account.balance_changes:
                 for balance_change in new_account.balance_changes:
                     if balance_change.block_access_index == tx1:
                         balance_indices[tx1] = True
-                        balance_change.block_access_index = HexNumber(tx2)
+                        balance_change.block_access_index = (
+                            ZeroPaddedHexNumber(tx2)
+                        )
                     elif balance_change.block_access_index == tx2:
                         balance_indices[tx2] = True
-                        balance_change.block_access_index = HexNumber(tx1)
+                        balance_change.block_access_index = (
+                            ZeroPaddedHexNumber(tx1)
+                        )
 
             # Swap in storage changes (nested structure)
             if new_account.storage_changes:
                 for storage_slot in new_account.storage_changes:
                     for storage_change in storage_slot.slot_changes:
                         if storage_change.block_access_index == tx1:
                             balance_indices[tx1] = True
-                            storage_change.block_access_index = HexNumber(tx2)
+                            storage_change.block_access_index = (
+                                ZeroPaddedHexNumber(tx2)
+                            )
                         elif storage_change.block_access_index == tx2:
                             balance_indices[tx2] = True
-                            storage_change.block_access_index = HexNumber(tx1)
+                            storage_change.block_access_index = (
+                                ZeroPaddedHexNumber(tx1)
+                            )
 
             # Note: storage_reads is just a list of StorageKey, no block_access_index to
             # swap
@@ -291,10 +306,14 @@ def transform(bal: BlockAccessList) -> BlockAccessList:
                 for code_change in new_account.code_changes:
                     if code_change.block_access_index == tx1:
                         code_indices[tx1] = True
-                        code_change.block_access_index = HexNumber(tx2)
+                        code_change.block_access_index = ZeroPaddedHexNumber(
+                            tx2
+                        )
                     elif code_change.block_access_index == tx2:
                         code_indices[tx2] = True
-                        code_change.block_access_index = HexNumber(tx1)
+                        code_change.block_access_index = ZeroPaddedHexNumber(
+                            tx1
+                        )
 
             new_root.append(new_account)
 

packages/testing/src/execution_testing/test_types/tests/test_block_access_list_expectation.py

@@ -567,7 +567,7 @@ def test_absent_values_nonce_changes(has_change_should_raise: bool) -> None:
 
     if has_change_should_raise:
         with pytest.raises(
-            Exception, match="Unexpected nonce change found at tx 0x2"
+            Exception, match="Unexpected nonce change found at tx 0x02"
         ):
             expectation.verify_against(actual_bal)
     else:
@@ -614,7 +614,7 @@ def test_absent_values_balance_changes(has_change_should_raise: bool) -> None:
     if has_change_should_raise:
         with pytest.raises(
             Exception,
-            match="Unexpected balance change found at tx 0x2",
+            match="Unexpected balance change found at tx 0x02",
         ):
             expectation.verify_against(actual_bal)
     else:
@@ -759,7 +759,7 @@ def test_absent_values_code_changes(has_change_should_raise: bool) -> None:
 
     if has_change_should_raise:
         with pytest.raises(
-            Exception, match="Unexpected code change found at tx 0x2"
+            Exception, match="Unexpected code change found at tx 0x02"
         ):
             expectation.verify_against(actual_bal)
     else:
@@ -898,7 +898,7 @@ def test_absent_values_with_multiple_tx_indices() -> None:
     )
 
     with pytest.raises(
-        Exception, match="Unexpected nonce change found at tx 0x1"
+        Exception, match="Unexpected nonce change found at tx 0x01"
     ):
         expectation_fail.verify_against(actual_bal)
 

packages/testing/src/execution_testing/test_types/tests/test_block_access_list_serialization.py

@@ -0,0 +1,86 @@
+"""
+Tests for BlockAccessList serialization format.
+
+These tests verify that BAL models serialize to JSON with the correct
+format, particularly zero-padded hex strings.
+"""
+
+from execution_testing.base_types import Address, Bytes
+from execution_testing.test_types.block_access_list import (
+    BalAccountChange,
+    BalBalanceChange,
+    BalCodeChange,
+    BalNonceChange,
+    BalStorageChange,
+    BalStorageSlot,
+    BlockAccessList,
+)
+
+
+def test_bal_serialization_roundtrip_zero_padded_hex() -> None:
+    """
+    Test that BAL serializes with zero-padded hex format and round-trips correctly.
+
+    This verifies that values like 12 serialize as "0x0c" (not "0xc"), which is
+    required for consistency with other test vector fields.
+    """
+    addr = Address(0xA)
+
+    original = BlockAccessList(
+        [
+            BalAccountChange(
+                address=addr,
+                nonce_changes=[
+                    BalNonceChange(block_access_index=1, post_nonce=12),
+                    BalNonceChange(block_access_index=2, post_nonce=255),
+                ],
+                balance_changes=[
+                    BalBalanceChange(block_access_index=1, post_balance=15),
+                ],
+                code_changes=[
+                    BalCodeChange(
+                        block_access_index=3, new_code=Bytes(b"\xde\xad")
+                    ),
+                ],
+                storage_changes=[
+                    BalStorageSlot(
+                        slot=12,
+                        slot_changes=[
+                            BalStorageChange(
+                                block_access_index=1, post_value=255
+                            ),
+                            BalStorageChange(
+                                block_access_index=2, post_value=4096
+                            ),
+                        ],
+                    ),
+                ],
+                storage_reads=[1, 15, 256],
+            )
+        ]
+    )
+
+    # Serialize to JSON
+    json_data = original.model_dump(mode="json")
+    account_data = json_data[0]
+
+    # Verify zero-padded hex format (0x0c not 0xc, 0x01 not 0x1)
+    assert account_data["nonce_changes"][0]["block_access_index"] == "0x01"
+    assert account_data["nonce_changes"][0]["post_nonce"] == "0x0c"
+    assert account_data["nonce_changes"][1]["post_nonce"] == "0xff"
+    assert account_data["balance_changes"][0]["post_balance"] == "0x0f"
+    assert account_data["code_changes"][0]["block_access_index"] == "0x03"
+    assert account_data["storage_changes"][0]["slot"] == "0x0c"
+    assert (
+        account_data["storage_changes"][0]["slot_changes"][0]["post_value"]
+        == "0xff"
+    )
+    assert (
+        account_data["storage_changes"][0]["slot_changes"][1]["post_value"]
+        == "0x1000"
+    )
+    assert account_data["storage_reads"] == ["0x01", "0x0f", "0x0100"]
+
+    # Round-trip: deserialize and verify equality
+    restored = BlockAccessList.model_validate(json_data)
+    assert restored == original