Add Altair networking helper tests

tests/core/pyspec/eth2spec/test/altair/unittests/networking/test_networking.py

@@ -0,0 +1,47 @@
+from eth2spec.test.context import (
+    with_altair_and_later,
+    spec_state_test,
+)
+from eth2spec.test.helpers.state import (
+    transition_to,
+)
+
+
+@with_altair_and_later
+@spec_state_test
+def test_get_sync_subcommittee_pubkeys_current_sync_committee(state, spec):
+    # Transition to the head of the next period
+    transition_to(spec, state, spec.SLOTS_PER_EPOCH * spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD)
+
+    next_slot_epoch = spec.compute_epoch_at_slot(state.slot + 1)
+    assert (
+        spec.compute_sync_committee_period(spec.get_current_epoch(state))
+        == spec.compute_sync_committee_period(next_slot_epoch)
+    )
+    sync_committee = state.current_sync_committee
+    sync_subcommittee_size = spec.SYNC_COMMITTEE_SIZE // spec.SYNC_COMMITTEE_SUBNET_COUNT
+    subcommittee_index = 1
+    i = subcommittee_index * sync_subcommittee_size
+
+    expect = sync_committee.pubkeys[i:i + sync_subcommittee_size]
+    assert spec.get_sync_subcommittee_pubkeys(state, subcommittee_index) == expect
+
+
+@with_altair_and_later
+@spec_state_test
+def test_get_sync_subcommittee_pubkeys_next_sync_committee(state, spec):
+    # Transition to the end of the current period
+    transition_to(spec, state, spec.SLOTS_PER_EPOCH * spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD - 1)
+
+    next_slot_epoch = spec.compute_epoch_at_slot(state.slot + 1)
+    assert (
+        spec.compute_sync_committee_period(spec.get_current_epoch(state))
+        != spec.compute_sync_committee_period(next_slot_epoch)
+    )
+    sync_committee = state.next_sync_committee
+    sync_subcommittee_size = spec.SYNC_COMMITTEE_SIZE // spec.SYNC_COMMITTEE_SUBNET_COUNT
+    subcommittee_index = 1
+    i = subcommittee_index * sync_subcommittee_size
+
+    expect = sync_committee.pubkeys[i:i + sync_subcommittee_size]
+    assert spec.get_sync_subcommittee_pubkeys(state, subcommittee_index) == expect