Use verify_sync flag appropriately for sync tests:

- With `-m blockchain_test_sync_only`, only generate the sync fixtures
- By default, fill blockchain, blockchain_engine, and IF verify_sync=True
  fill blockchain_engine_sync test.

Author: fselmo

src/ethereum_test_specs/blockchain.py

@@ -1,7 +1,7 @@
 """Ethereum blockchain test spec definition and filler."""
 
 from pprint import pprint
-from typing import Any, Callable, ClassVar, Dict, Generator, List, Optional, Sequence, Tuple, Type
+from typing import Any, Callable, ClassVar, Dict, Generator, List, Sequence, Tuple, Type
 
 import pytest
 from pydantic import ConfigDict, Field, field_validator
@@ -404,6 +404,8 @@ class BlockchainTest(BaseTest):
     post: Alloc
     blocks: List[Block]
     genesis_environment: Environment = Field(default_factory=Environment)
+    # If set to True, generate a BlockchainEngineSyncFixture to
+    # verify syncing between clients.
     verify_sync: bool = False
     chain_id: int = 1
     exclude_full_post_state_in_output: bool = False
@@ -429,7 +431,7 @@ class BlockchainTest(BaseTest):
     supported_markers: ClassVar[Dict[str, str]] = {
         "blockchain_test_engine_only": "Only generate a blockchain test engine fixture",
         "blockchain_test_only": "Only generate a blockchain test fixture",
-        "blockchain_engine_sync_test": "Generate a blockchain engine sync test fixture",
+        "blockchain_test_sync_only": "Only generate a blockchain test sync fixture",
     }
 
     @classmethod
@@ -446,12 +448,11 @@ def discard_fixture_format_by_marks(
             return fixture_format != BlockchainFixture
         if "blockchain_test_engine_only" in marker_names:
             return fixture_format != BlockchainEngineFixture
-        if "blockchain_engine_sync_test" in marker_names:
-            # Only generate sync fixture when marker is present
-            return fixture_format != BlockchainEngineSyncFixture
-        else:
-            # When sync marker is NOT present, exclude sync fixture
-            return fixture_format == BlockchainEngineSyncFixture
+        # Note: Don't check for ``blockchain_test_sync_only`` here because the marker
+        # is added dynamically for tests with ``verify_sync=True``. The ``generate()``
+        # method handles skipping sync fixtures when ``verify_sync=False``.
+
+        return False
 
     def get_genesis_environment(self, fork: Fork) -> Environment:
         """Get the genesis environment for pre-allocation groups."""
@@ -764,27 +765,11 @@ def make_hive_fixture(
 
         self.verify_post_state(t8n, t8n_state=alloc)
 
-        sync_payload: Optional[FixtureEngineNewPayload] = None
-        # Only include sync_payload for BlockchainEngineSyncFixture
-        if fixture_format == BlockchainEngineSyncFixture:
-            # Test is marked for syncing verification.
-            # Most clients require the header to start the sync process, so we create an empty
-            # block on top of the last block of the test to send it as new payload and trigger
-            # the sync process.
-            sync_built_block = self.generate_block_data(
-                t8n=t8n,
-                fork=fork,
-                block=Block(),
-                previous_env=env,
-                previous_alloc=alloc,
-                last_block=False,
-            )
-            sync_payload = sync_built_block.get_fixture_engine_new_payload()
-
-        # Create base fixture data
+        # Create base fixture data, common to all fixture formats
         fixture_data = {
             "fork": fork,
             "genesis": genesis.header,
+            "payloads": fixture_payloads,
             "last_block_hash": head_hash,
             "post_state_hash": alloc.state_root()
             if self.exclude_full_post_state_in_output
@@ -802,19 +787,30 @@ def make_hive_fixture(
             # and prepare for state diff optimization
             fixture_data.update(
                 {
-                    "payloads": fixture_payloads,
-                    "sync_payload": sync_payload,
                     "post_state": alloc if not self.exclude_full_post_state_in_output else None,
                     "pre_hash": "",  # Will be set by BaseTestWrapper
                 }
             )
             return BlockchainEngineXFixture(**fixture_data)
         elif fixture_format == BlockchainEngineSyncFixture:
-            # For sync fixture format
+            # Sync fixture format
+            assert genesis.header.block_hash != head_hash, (
+                "Invalid payload tests negative test via sync is not supported yet."
+            )
+            # Most clients require the header to start the sync process, so we create an empty
+            # block on top of the last block of the test to send it as new payload and trigger the
+            # sync process.
+            sync_built_block = self.generate_block_data(
+                t8n=t8n,
+                fork=fork,
+                block=Block(),
+                previous_env=env,
+                previous_alloc=alloc,
+                last_block=False,
+            )
             fixture_data.update(
                 {
-                    "payloads": fixture_payloads,
-                    "sync_payload": sync_payload,
+                    "sync_payload": sync_built_block.get_fixture_engine_new_payload(),
                     "pre": pre,
                     "post_state": alloc if not self.exclude_full_post_state_in_output else None,
                 }
@@ -824,8 +820,6 @@ def make_hive_fixture(
             # Standard engine fixture
             fixture_data.update(
                 {
-                    "payloads": fixture_payloads,
-                    "sync_payload": sync_payload,
                     "pre": pre,
                     "post_state": alloc if not self.exclude_full_post_state_in_output else None,
                 }
@@ -839,6 +833,10 @@ def generate(
         fixture_format: FixtureFormat,
     ) -> BaseFixture:
         """Generate the BlockchainTest fixture."""
+        # Skip sync fixture generation if verify_sync is False
+        if fixture_format == BlockchainEngineSyncFixture and not self.verify_sync:
+            raise pytest.skip("Skipping sync fixture for test without verify_sync=True")
+
         t8n.reset_traces()
         if fixture_format in [
             BlockchainEngineFixture,

src/pytest_plugins/filler/filler.py

@@ -26,6 +26,7 @@
 from ethereum_test_base_types import Account, Address, Alloc, ReferenceSpec
 from ethereum_test_fixtures import (
     BaseFixture,
+    BlockchainEngineSyncFixture,
     BlockchainEngineXFixture,
     FixtureCollector,
     FixtureConsumer,
@@ -336,6 +337,11 @@ def pytest_configure(config):
         called before the pytest-html plugin's pytest_configure to ensure that
         it uses the modified `htmlpath` option.
     """
+    # Register custom markers
+    config.addinivalue_line(
+        "markers", "blockchain_test_sync_only: Only generate blockchain sync test fixtures"
+    )
+
     # Modify the block gas limit if specified.
     if config.getoption("block_gas_limit"):
         EnvironmentDefaults.gas_limit = config.getoption("block_gas_limit")
@@ -1113,7 +1119,13 @@ def pytest_collection_modifyitems(
 
     These can't be handled in this plugins pytest_generate_tests() as the fork
     parametrization occurs in the forks plugin.
+
+    Also dynamically adds custom markers to tests based on their parameters (e.g.,
+    `blockchain_test_sync_only` for tests that have `verify_sync=True` in their
+    `blockchain_test` parameters).
     """
+    import inspect
+
     items_for_removal = []
     for i, item in enumerate(items):
         params: Dict[str, Any] | None = None
@@ -1133,7 +1145,28 @@ def pytest_collection_modifyitems(
         if not fixture_format.supports_fork(fork):
             items_for_removal.append(i)
             continue
+
+        # Check if test has ``verify_sync=True`` and add marker if it does
+        # This needs to happen before we check ``discard_fixture_format_by_marks``
+        if hasattr(item, "function"):
+            try:
+                test_func = item.function
+                source = inspect.getsource(test_func)
+                if "verify_sync=True" in source:
+                    # Add the marker so pytest can filter it with `-m`
+                    item.add_marker(pytest.mark.blockchain_test_sync_only)
+            except Exception:
+                pass  # If we can't inspect, just continue
+
         markers = list(item.iter_markers())
+        # Check for ``-m blockchain_test_sync_only`` and only fill sync tests
+        if (
+            config.getoption("-m") == "blockchain_test_sync_only"
+            and "blockchain_test_sync_only" in [m.name for m in markers]
+            and fixture_format != BlockchainEngineSyncFixture
+        ):
+            items_for_removal.append(i)
+            continue
         if spec_type.discard_fixture_format_by_marks(fixture_format, fork, markers):
             items_for_removal.append(i)
             continue

tests/osaka/eip7934_block_rlp_limit/test_max_block_rlp_size.py

@@ -389,7 +389,6 @@ def _exact_size_transactions_impl(
         pytest.param(1, id="max_rlp_size_plus_1_byte", marks=pytest.mark.exception_test),
     ],
 )
-@pytest.mark.blockchain_engine_sync_test
 def test_block_at_rlp_size_limit_boundary(
     blockchain_test: BlockchainTestFiller,
     pre: Alloc,
@@ -443,7 +442,6 @@ def test_block_at_rlp_size_limit_boundary(
 
 
 @pytest.mark.with_all_typed_transactions
-@pytest.mark.blockchain_engine_sync_test
 def test_block_rlp_size_at_limit_with_all_typed_transactions(
     blockchain_test: BlockchainTestFiller,
     pre: Alloc,
@@ -453,7 +451,6 @@ def test_block_rlp_size_at_limit_with_all_typed_transactions(
     block_size_limit: int,
     env: Environment,
     typed_transaction: Transaction,
-    request: pytest.FixtureRequest,
 ) -> None:
     """Test the block RLP size limit with all transaction types."""
     transactions, gas_used = exact_size_transactions(
@@ -483,7 +480,6 @@ def test_block_rlp_size_at_limit_with_all_typed_transactions(
     )
 
 
-@pytest.mark.blockchain_engine_sync_test
 def test_block_at_rlp_limit_with_logs(
     blockchain_test: BlockchainTestFiller,
     pre: Alloc,