refactor(bal): Split BAL into two classes

- Use a root model class for the t8n BAL model. This lets us stick
  closer to the EIP definition where the BAL itself is a list.
- The class doesn't need to be `RLPSerializable`, just have
  simple instructions to serialize its elements (`rlp()`).
- Create a `BlockAccessListExpectation` class to represent the
  expected BAL for a given block. This class can describe different
  expectations for the test cases, such as defining mutations to
  be used for invalid tests.

Author: fselmo

src/ethereum_clis/types.py

@@ -12,8 +12,13 @@
     TransactionException,
     UndefinedException,
 )
-from ethereum_test_types import Alloc, Environment, Transaction, TransactionReceipt
-from ethereum_test_types.block_access_list import BlockAccessList
+from ethereum_test_types import (
+    Alloc,
+    BlockAccessList,
+    Environment,
+    Transaction,
+    TransactionReceipt,
+)
 
 
 class TransactionExceptionWithMessage(ExceptionWithMessage[TransactionException]):

src/ethereum_test_specs/blockchain.py

@@ -52,7 +52,7 @@
 from ethereum_test_fixtures.common import FixtureBlobSchedule
 from ethereum_test_forks import Fork
 from ethereum_test_types import Alloc, Environment, Removable, Requests, Transaction, Withdrawal
-from ethereum_test_types.block_access_list import BlockAccessList
+from ethereum_test_types.block_access_list import BlockAccessList, BlockAccessListExpectation
 
 from .base import BaseTest, OpMode, verify_result
 from .debugging import print_traces
@@ -426,11 +426,11 @@ class BlockchainTest(BaseTest):
     Exclude the post state from the fixture output.
     In this case, the state verification is only performed based on the state root.
     """
-    expected_block_access_list: Any | None = None  # Will be BAL type
+    expected_block_access_list: BlockAccessListExpectation | None = None
     """
     Expected block access list for verification.
     If set, verifies that the block access list returned by the client matches expectations.
-    Use the BAL builder API to construct expectations.
+    Use BlockAccessListExpectation to define partial validation expectations.
     """
 
     supported_fixture_formats: ClassVar[Sequence[FixtureFormat | LabeledFixtureFormat]] = [
@@ -691,7 +691,7 @@ def verify_post_state(self, t8n, t8n_state: Alloc, expected_state: Alloc | None
             raise e
 
     def verify_block_access_list(
-        self, actual_bal: BlockAccessList | None, expected_bal: Any | None
+        self, actual_bal: BlockAccessList | None, expected_bal: BlockAccessListExpectation | None
     ):
         """
         Verify that the actual block access list matches expectations.
@@ -704,15 +704,9 @@ def verify_block_access_list(
         if expected_bal is None:
             return
 
-        if not isinstance(expected_bal, BlockAccessList):
-            raise Exception(
-                f"Invalid expected_bal type: {type(expected_bal)}. Use BlockAccessList."
-            )
-
         if actual_bal is None:
             raise Exception("Expected block access list but got none.")
 
-        # Verify using the BlockAccessList's verification method
         try:
             expected_bal.verify_against(actual_bal)
         except Exception as e:

src/ethereum_test_types/__init__.py

@@ -10,6 +10,7 @@
     BalStorageChange,
     BalStorageSlot,
     BlockAccessList,
+    BlockAccessListExpectation,
 )
 from .block_types import (
     Environment,
@@ -52,6 +53,7 @@
     "BalStorageSlot",
     "Blob",
     "BlockAccessList",
+    "BlockAccessListExpectation",
     "ConsolidationRequest",
     "DepositRequest",
     "Environment",

src/ethereum_test_types/block_access_list.py

@@ -5,14 +5,16 @@
 these are simple data classes that can be composed together.
 """
 
-from typing import Any, ClassVar, Dict, List
+from typing import Any, ClassVar, List
 
+import ethereum_rlp as eth_rlp
 from pydantic import Field
 
 from ethereum_test_base_types import (
     Address,
     Bytes,
     CamelModel,
+    EthereumTestRootModel,
     HexNumber,
     Number,
     RLPSerializable,
@@ -98,56 +100,61 @@ class BalAccountChange(CamelModel, RLPSerializable):
     ]
 
 
-class BlockAccessList(CamelModel, RLPSerializable):
+class BlockAccessList(EthereumTestRootModel[List[BalAccountChange]]):
     """
-    Expected Block Access List for verification.
+    Block Access List for t8n tool communication and fixtures.
+
+    This model represents the BAL exactly as defined in EIP-7928 - it is itself a list
+    of account changes (root model), not a container. Used for:
+    - Communication with t8n tools
+    - Fixture generation
+    - RLP encoding for hash verification
 
     Example:
-        expected_block_access_list = BlockAccessList(
+        bal = BlockAccessList([
+            BalAccountChange(address=alice, nonce_changes=[...]),
+            BalAccountChange(address=bob, balance_changes=[...])
+        ])
+
+    """
+
+    root: List[BalAccountChange] = Field(default_factory=list)
+
+    def to_list(self) -> List[Any]:
+        """Return the list for RLP encoding per EIP-7928."""
+        return to_serializable_element(self.root)
+
+    def rlp(self) -> Bytes:
+        """Return the RLP encoded block access list for hash verification."""
+        return Bytes(eth_rlp.encode(self.to_list()))
+
+
+class BlockAccessListExpectation(CamelModel):
+    """
+    Block Access List expectation model for test writing.
+
+    This model is used to define expected BAL values in tests. It supports:
+    - Partial validation (only checks explicitly set fields)
+    - Convenient test syntax with named parameters
+    - Verification against actual BAL from t8n
+
+    Example:
+        # In test definition
+        expected_block_access_list = BlockAccessListExpectation(
             account_changes=[
                 BalAccountChange(
                     address=alice,
-                    nonce_changes=[
-                        BalNonceChange(tx_index=0, post_nonce=1)
-                    ],
-                    balance_changes=[
-                        BalBalanceChange(tx_index=0, post_balance=9000)
-                    ]
-                ),
-                BalAccountChange(
-                    address=bob,
-                    balance_changes=[
-                        BalBalanceChange(tx_index=0, post_balance=100)
-                    ],
-                    code_changes=[
-                        BalCodeChange(tx_index=0, new_code=b"0x1234")
-                    ],
-                ),
+                    nonce_changes=[BalNonceChange(tx_index=1, post_nonce=1)]
+                )
             ]
         )
 
     """
 
     account_changes: List[BalAccountChange] = Field(
-        default_factory=list, description="List of account changes in the block"
+        default_factory=list, description="Expected account changes to verify"
     )
 
-    rlp_fields: ClassVar[List[str]] = ["account_changes"]
-
-    def to_list(self, signing: bool = False) -> List[Any]:
-        """
-        Override to_list to return the account changes list directly.
-
-        The BlockAccessList IS the list of account changes, not a container
-        that contains a list, per EIP-7928.
-        """
-        # Return the list of accounts directly, not wrapped in another list
-        return to_serializable_element(self.account_changes)
-
-    def to_dict(self) -> Dict[str, Any]:
-        """Convert to dictionary for serialization."""
-        return self.model_dump(exclude_none=True)
-
     def verify_against(self, actual_bal: "BlockAccessList") -> None:
         """
         Verify that the actual BAL from the client matches this expected BAL.
@@ -159,7 +166,7 @@ def verify_against(self, actual_bal: "BlockAccessList") -> None:
             Exception: If verification fails
 
         """
-        actual_accounts_by_addr = {acc.address: acc for acc in actual_bal.account_changes}
+        actual_accounts_by_addr = {acc.address: acc for acc in actual_bal.root}
         expected_accounts_by_addr = {acc.address: acc for acc in self.account_changes}
 
         # Check for missing accounts

src/pytest_plugins/eels_resolutions.json

@@ -55,6 +55,6 @@
       "Amsterdam": {
           "git_url": "https://github.com/fselmo/execution-specs.git",
           "branch": "feat/amsterdam-fork-and-block-access-lists",
-          "commit": "59ff2946ca30879079b2ef2b601ae09106ca08f7"
+          "commit": "f4c49309e90e74b51d043b06c045735b54e997b0"
       }
 }

tests/amsterdam/eip7928_block_level_access_lists/test_block_access_lists.py

@@ -18,7 +18,7 @@
     BalNonceChange,
     BalStorageChange,
     BalStorageSlot,
-    BlockAccessList,
+    BlockAccessListExpectation,
 )
 
 from .spec import ref_spec_7928
@@ -51,7 +51,7 @@ def test_bal_nonce_changes(
             alice: Account(nonce=1),
             bob: Account(balance=100),
         },
-        expected_block_access_list=BlockAccessList(
+        expected_block_access_list=BlockAccessListExpectation(
             account_changes=[
                 BalAccountChange(
                     address=alice,
@@ -103,7 +103,7 @@ def test_bal_balance_changes(
             alice: Account(nonce=1, balance=alice_final_balance),
             bob: Account(balance=100),
         },
-        expected_block_access_list=BlockAccessList(
+        expected_block_access_list=BlockAccessListExpectation(
             account_changes=[
                 BalAccountChange(
                     address=alice,
@@ -146,7 +146,7 @@ def test_bal_storage_writes(
             alice: Account(nonce=1),
             storage_contract: Account(storage={0x01: 0x42}),
         },
-        expected_block_access_list=BlockAccessList(
+        expected_block_access_list=BlockAccessListExpectation(
             account_changes=[
                 BalAccountChange(
                     address=storage_contract,
@@ -189,7 +189,7 @@ def test_bal_storage_reads(
             alice: Account(nonce=1),
             storage_contract: Account(storage={0x01: 0x42}),
         },
-        expected_block_access_list=BlockAccessList(
+        expected_block_access_list=BlockAccessListExpectation(
             account_changes=[
                 BalAccountChange(
                     address=storage_contract,
@@ -259,7 +259,7 @@ def test_bal_code_changes(
                 storage={},
             ),
         },
-        expected_block_access_list=BlockAccessList(
+        expected_block_access_list=BlockAccessListExpectation(
             account_changes=[
                 BalAccountChange(
                     address=alice,