Add basic test for invalid sync committee bits

tests/core/pyspec/eth2spec/test/lightclient_patch/block_processing/test_process_sync_committee.py

@@ -0,0 +1,36 @@
+import random
+from eth2spec.test.helpers.block import (
+    build_empty_block_for_next_slot,
+)
+from eth2spec.test.lightclient_patch.helpers import (
+    compute_aggregate_sync_committee_signature,
+)
+from eth2spec.test.context import (
+    PHASE0, PHASE1,
+    expect_assertion_error,
+    with_all_phases_except,
+    spec_state_test,
+)
+
+
+@with_all_phases_except([PHASE0, PHASE1])
+@spec_state_test
+def test_invalid_sync_committee_bits(spec, state):
+    committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+    random_participant = random.choice(committee)
+
+    yield 'pre', state
+
+    block = build_empty_block_for_next_slot(spec, state)
+    # Exclude one participant whose signature was included.
+    block.body.sync_committee_bits = [index != random_participant for index in committee]
+    block.body.sync_committee_signature = compute_aggregate_sync_committee_signature(
+        spec,
+        state,
+        block.slot - 1,
+        committee,
+    )
+
+    yield 'blocks', [block]
+    expect_assertion_error(lambda: spec.process_sync_committee(state, block.body))
+    yield 'post', None