Allow extending LC merkle proof tests

Currently, `test_single_merkle_proof` only supports `BeaconState` tests.
For future tests, different object classes are desirable. Update format
to allow testing other objects as well.

tests/core/pyspec/eth2spec/test/altair/light_client/test_single_merkle_proof.py

@@ -7,8 +7,10 @@ from eth2spec.test.context import (
 @with_altair_and_later
 @spec_state_test
 def test_current_sync_committee_merkle_proof(spec, state):
-    yield "state", state
+    yield "object_class", "meta", "BeaconState"
-    current_sync_committee_branch = spec.compute_merkle_proof_for_state(state, spec.CURRENT_SYNC_COMMITTEE_INDEX)
+    yield "object", state
+    current_sync_committee_branch = \
+        spec.compute_merkle_proof_for_state(state, spec.CURRENT_SYNC_COMMITTEE_INDEX)
     yield "proof", {
         "leaf": "0x" + state.current_sync_committee.hash_tree_root().hex(),
         "leaf_index": spec.CURRENT_SYNC_COMMITTEE_INDEX,
@@ -26,8 +28,10 @@ def test_current_sync_committee_merkle_proof(spec, state):
 @with_altair_and_later
 @spec_state_test
 def test_next_sync_committee_merkle_proof(spec, state):
-    yield "state", state
+    yield "object_class", "meta", "BeaconState"
-    next_sync_committee_branch = spec.compute_merkle_proof_for_state(state, spec.NEXT_SYNC_COMMITTEE_INDEX)
+    yield "object", state
+    next_sync_committee_branch = \
+        spec.compute_merkle_proof_for_state(state, spec.NEXT_SYNC_COMMITTEE_INDEX)
     yield "proof", {
         "leaf": "0x" + state.next_sync_committee.hash_tree_root().hex(),
         "leaf_index": spec.NEXT_SYNC_COMMITTEE_INDEX,
@@ -45,8 +49,10 @@ def test_next_sync_committee_merkle_proof(spec, state):
 @with_altair_and_later
 @spec_state_test
 def test_finality_root_merkle_proof(spec, state):
-    yield "state", state
+    yield "object_class", "meta", "BeaconState"
-    finality_branch = spec.compute_merkle_proof_for_state(state, spec.FINALIZED_ROOT_INDEX)
+    yield "object", state
+    finality_branch = \
+        spec.compute_merkle_proof_for_state(state, spec.FINALIZED_ROOT_INDEX)
     yield "proof", {
         "leaf": "0x" + state.finalized_checkpoint.root.hex(),
         "leaf_index": spec.FINALIZED_ROOT_INDEX,

tests/formats/light_client/single_merkle_proof.md

@@ -5,13 +5,19 @@ generation and verification of merkle proofs based on static data.
 
 ## Test case format
 
-### `state.ssz_snappy`
+### `meta.yaml`
 
-An SSZ-snappy encoded `BeaconState` object from which other data is generated.
+```yaml
+object_class: string  -- 'BeaconState'
+```
+
+### `object.yaml`
+
+A SSZ-snappy encoded object of type `object_class` from which other data is generated.
 
 ### `proof.yaml`
 
-A proof of the leaf value (a merkle root) at generalized-index `leaf_index` in the given `state`.
+A proof of the leaf value (a merkle root) at generalized-index `leaf_index` in the given `object`.
 
 ```yaml
 leaf: Bytes32            # string, hex encoded, with 0x prefix
@@ -23,6 +29,6 @@ branch: list of Bytes32  # list, each element is a string, hex encoded, with 0x
 
 A test-runner can implement the following assertions:
 - Check that `is_valid_merkle_branch` confirms `leaf` at `leaf_index` to verify
-  against `has_tree_root(state)` and `proof`.
+  against `hash_tree_root(object)` and `branch`.
 - If the implementation supports generating merkle proofs, check that the
-  self-generated proof matches the `proof` provided with the test.
+  self-generated proof matches the `branch` provided with the test.