test: add test vectors for verifying multi message proofs (leanEthereum#810)

* test(testing): add VerifyMultiMessageProofsTest fixture

Mirror the single-message fixture for the Type-2 multi-message aggregate
primitive: per-component validator lists, per-component attestation data,
emitted parallel lists of messages, slots, public keys, and aggregation
bits, plus the merged proof bytes.

Three tampers target one component at a time:
- RebindComponentToAlternateHeadRoot regenerates one component against an
  alternate head root and re-merges, so the emitted layout stays honest
  but the merged proof bytes carry the off-target binding.
- IncrementComponentSlot bumps one component's emitted slot past its
  bound slot.
- SwapComponentParticipantPublicKey swaps one participant's key for
  another validator's, breaking the layout the merged proof verifies
  against.

* test(consensus): add multi-message verify vectors for lstar

Three positive vectors covering two- and three-component bundles with
single-, four-, and mixed-sized participant lists; three rejection
vectors covering wrong message, wrong slot, and wrong public key applied
to one component at a time.

* test(testing): cover multi-message-specific rejection paths and dedup the verify ladder

Add the failure modes that only a multi-message (Type-2) proof can suffer,
which the initial vector set did not reach:

- SwapComponentMessageBindings transposes two components' emitted
  message-slot bindings after an honest merge, with distinct head roots per
  component, so each component's proof faces the other's binding. This is the
  canonical Type-2 attack the positional binding exists to reject.
- DropComponentMessageBinding removes one component's binding while keeping
  its keys, exercising the verifier's binding-count guard.

Add two valid vectors for parity with the single-message suite: a single
component bundle (the n=1 boundary) and a non-contiguous committee whose
aggregation bits resolve to [1, 0, 1, 1].

Factor the identical expectation-comparison ladder into
BaseConsensusFixture.assert_expected_outcome and reuse it from both verify
fixtures. Hoist the repeated component-index range check into a helper, and
guard the slot-increment tamper against landing on a neighbour's slot.

Inline the per-test attestation data to match the single-message sibling
files, rename the ambiguous swap field to participant_index, and correct the
union docstring.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Thomas Coratger <60488569+tcoratger@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

packages/testing/src/consensus_testing/__init__.py

@@ -7,18 +7,24 @@
 from .test_fixtures import (
     ApiEndpointTest,
     BaseConsensusFixture,
+    DropComponentMessageBinding,
     ForkChoiceTest,
     GossipsubHandlerTest,
+    IncrementComponentSlot,
     IncrementEmittedSlot,
     JustifiabilityTest,
     NetworkingCodecTest,
     PoseidonPermutationTest,
+    RebindComponentToAlternateHeadRoot,
     RebindToAlternateHeadRoot,
     SlotClockTest,
     SSZTest,
     StateTransitionTest,
+    SwapComponentMessageBindings,
+    SwapComponentParticipantPublicKey,
     SwapParticipantPublicKey,
     SyncTest,
+    VerifyMultiMessageProofsTest,
     VerifySignaturesTest,
     VerifySingleMessageProofsTest,
 )
@@ -42,6 +48,7 @@
 StateTransitionTestFiller = Type[StateTransitionTest]
 ForkChoiceTestFiller = Type[ForkChoiceTest]
 VerifySingleMessageProofsTestFiller = Type[VerifySingleMessageProofsTest]
+VerifyMultiMessageProofsTestFiller = Type[VerifyMultiMessageProofsTest]
 VerifySignaturesTestFiller = Type[VerifySignaturesTest]
 SSZTestFiller = Type[SSZTest]
 NetworkingCodecTestFiller = Type[NetworkingCodecTest]
@@ -70,6 +77,12 @@
     "RebindToAlternateHeadRoot",
     "IncrementEmittedSlot",
     "SwapParticipantPublicKey",
+    "VerifyMultiMessageProofsTest",
+    "RebindComponentToAlternateHeadRoot",
+    "IncrementComponentSlot",
+    "SwapComponentParticipantPublicKey",
+    "SwapComponentMessageBindings",
+    "DropComponentMessageBinding",
     "VerifySignaturesTest",
     "SSZTest",
     "NetworkingCodecTest",
@@ -94,6 +107,7 @@
     "StateTransitionTestFiller",
     "ForkChoiceTestFiller",
     "VerifySingleMessageProofsTestFiller",
+    "VerifyMultiMessageProofsTestFiller",
     "VerifySignaturesTestFiller",
     "SSZTestFiller",
     "NetworkingCodecTestFiller",

packages/testing/src/consensus_testing/test_fixtures/__init__.py

@@ -11,6 +11,14 @@
 from .ssz import SSZTest
 from .state_transition import StateTransitionTest
 from .sync import SyncTest
+from .verify_multi_message_proofs import (
+    DropComponentMessageBinding,
+    IncrementComponentSlot,
+    RebindComponentToAlternateHeadRoot,
+    SwapComponentMessageBindings,
+    SwapComponentParticipantPublicKey,
+    VerifyMultiMessageProofsTest,
+)
 from .verify_signatures import VerifySignaturesTest
 from .verify_single_message_proofs import (
     IncrementEmittedSlot,
@@ -27,6 +35,12 @@
     "RebindToAlternateHeadRoot",
     "IncrementEmittedSlot",
     "SwapParticipantPublicKey",
+    "VerifyMultiMessageProofsTest",
+    "RebindComponentToAlternateHeadRoot",
+    "IncrementComponentSlot",
+    "SwapComponentParticipantPublicKey",
+    "SwapComponentMessageBindings",
+    "DropComponentMessageBinding",
     "VerifySignaturesTest",
     "SSZTest",
     "NetworkingCodecTest",

packages/testing/src/consensus_testing/test_fixtures/base.py

@@ -44,3 +44,31 @@ def serialize_exception(self, value: type[Exception] | None) -> str | None:
         if value is None:
             return None
         return value.__name__
+
+    def assert_expected_outcome(self, exception_raised: Exception | None) -> None:
+        """Compare a self-verification outcome against the configured expectation.
+
+        A fixture that self-verifies its own output catches the verifier exception.
+        It then hands the caught exception here to decide pass or fail.
+
+        Args:
+            exception_raised: The exception the verifier raised, or None on success.
+
+        Raises:
+            AssertionError: When the outcome disagrees with the expectation.
+        """
+        # No expectation means the bundle is honest and must verify.
+        if self.expect_exception is None:
+            if exception_raised is not None:
+                raise AssertionError(f"Verifier rejected an honest bundle: {exception_raised}")
+        # An expectation that produced no exception means the tamper went undetected.
+        elif exception_raised is None:
+            raise AssertionError(
+                f"Expected {self.expect_exception.__name__} but verification succeeded"
+            )
+        # A wrong exception type means the rejection fired for the wrong reason.
+        elif not isinstance(exception_raised, self.expect_exception):
+            raise AssertionError(
+                f"Expected {self.expect_exception.__name__} but got "
+                f"{type(exception_raised).__name__}: {exception_raised}"
+            )