diff --git a/setup.py b/setup.py
index 514f75c50..0a64307c0 100644
--- a/setup.py
+++ b/setup.py
@@ -695,7 +695,7 @@ setup(
         "py_ecc==5.2.0",
         "milagro_bls_binding==1.6.3",
         "dataclasses==0.6",
-        "remerkleable==0.1.18",
+        "remerkleable==0.1.19",
         "ruamel.yaml==0.16.5",
         "lru-dict==1.1.6",
     ]
diff --git a/tests/core/pyspec/eth2spec/test/altair/unittests/validator/__init__.py b/tests/core/pyspec/eth2spec/test/altair/unittests/validator/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/core/pyspec/eth2spec/test/altair/unittests/validator/test_validator.py b/tests/core/pyspec/eth2spec/test/altair/unittests/validator/test_validator.py
new file mode 100644
index 000000000..244e1aa7e
--- /dev/null
+++ b/tests/core/pyspec/eth2spec/test/altair/unittests/validator/test_validator.py
@@ -0,0 +1,166 @@
+import random
+from collections import defaultdict
+from eth2spec.utils.ssz.ssz_typing import Bitvector
+from eth2spec.test.helpers.block import build_empty_block
+from eth2spec.test.helpers.keys import pubkey_to_privkey
+from eth2spec.test.helpers.state import transition_to
+from eth2spec.utils import bls
+from eth2spec.utils.bls import only_with_bls
+from eth2spec.test.context import (
+    PHASE0,
+    with_all_phases_except,
+    with_state,
+)
+
+rng = random.Random(1337)
+
+
+def ensure_assignments_in_sync_committee(
+    spec, state, epoch, sync_committee, active_pubkeys
+):
+    assert len(sync_committee.pubkeys) >= 3
+    some_pubkeys = rng.sample(sync_committee.pubkeys, 3)
+    for pubkey in some_pubkeys:
+        validator_index = active_pubkeys.index(pubkey)
+        assert spec.is_assigned_to_sync_committee(state, epoch, validator_index)
+
+
+@with_all_phases_except([PHASE0])
+@with_state
+def test_is_assigned_to_sync_committee(phases, spec, state):
+    epoch = spec.get_current_epoch(state)
+    validator_indices = spec.get_active_validator_indices(state, epoch)
+    validator_count = len(validator_indices)
+
+    query_epoch = epoch + 1
+    next_query_epoch = query_epoch + spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD
+    active_pubkeys = [state.validators[index].pubkey for index in validator_indices]
+
+    ensure_assignments_in_sync_committee(
+        spec, state, query_epoch, state.current_sync_committee, active_pubkeys
+    )
+    ensure_assignments_in_sync_committee(
+        spec, state, next_query_epoch, state.next_sync_committee, active_pubkeys
+    )
+
+    sync_committee_pubkeys = set(
+        list(state.current_sync_committee.pubkeys)
+        + list(state.next_sync_committee.pubkeys)
+    )
+    disqualified_pubkeys = set(
+        filter(lambda key: key not in sync_committee_pubkeys, active_pubkeys)
+    )
+    # NOTE: only check `disqualified_pubkeys` if SYNC_COMMITEE_SIZE < validator count
+    if disqualified_pubkeys:
+        sample_size = 3
+        assert validator_count >= sample_size
+        some_pubkeys = rng.sample(disqualified_pubkeys, sample_size)
+        for pubkey in some_pubkeys:
+            validator_index = active_pubkeys.index(pubkey)
+            is_current = spec.is_assigned_to_sync_committee(
+                state, query_epoch, validator_index
+            )
+            is_next = spec.is_assigned_to_sync_committee(
+                state, next_query_epoch, validator_index
+            )
+            is_current_or_next = is_current or is_next
+            assert not is_current_or_next
+
+
+def _get_sync_committee_signature(
+    spec,
+    state,
+    target_slot,
+    target_block_root,
+    subcommittee_index,
+    index_in_subcommittee,
+):
+    subcommittee_size = spec.SYNC_COMMITTEE_SIZE // spec.SYNC_COMMITTEE_SUBNET_COUNT
+    sync_committee_index = (
+        subcommittee_index * subcommittee_size + index_in_subcommittee
+    )
+    pubkey = state.current_sync_committee.pubkeys[sync_committee_index]
+    privkey = pubkey_to_privkey[pubkey]
+
+    domain = spec.get_domain(
+        state,
+        spec.DOMAIN_SYNC_COMMITTEE,
+    )
+    signing_data = spec.compute_signing_root(target_block_root, domain)
+    return bls.Sign(privkey, spec.hash_tree_root(signing_data))
+
+
+@only_with_bls()
+@with_all_phases_except([PHASE0])
+@with_state
+def test_process_sync_committee_contributions(phases, spec, state):
+    # skip over slots at genesis
+    transition_to(spec, state, state.slot + 3)
+
+    # build a block and attempt to assemble a sync aggregate
+    # from some sync committee contributions
+    block = build_empty_block(spec, state)
+    previous_slot = state.slot - 1
+    target_block_root = spec.get_block_root_at_slot(state, previous_slot)
+    aggregation_bits = Bitvector[
+        spec.SYNC_COMMITTEE_SIZE // spec.SYNC_COMMITTEE_SUBNET_COUNT
+    ]()
+    aggregation_index = 0
+    aggregation_bits[aggregation_index] = True
+
+    contributions = [
+        spec.SyncCommitteeContribution(
+            slot=block.slot,
+            beacon_block_root=target_block_root,
+            subcommittee_index=i,
+            aggregation_bits=aggregation_bits,
+            signature=_get_sync_committee_signature(
+                spec, state, previous_slot, target_block_root, i, aggregation_index
+            ),
+        )
+        for i in range(spec.SYNC_COMMITTEE_SUBNET_COUNT)
+    ]
+
+    # ensure the block has an empty sync aggregate...
+    empty_sync_aggregate = spec.SyncAggregate()
+    empty_sync_aggregate.sync_committee_signature = spec.G2_POINT_AT_INFINITY
+    assert block.body.sync_aggregate == empty_sync_aggregate
+    spec.process_sync_committee_contributions(block, set(contributions))
+
+    # and that after processing, it is no longer empty
+    assert len(block.body.sync_aggregate.sync_committee_bits) != 0
+    assert (
+        block.body.sync_aggregate.sync_committee_signature != spec.G2_POINT_AT_INFINITY
+    )
+    # moreover, ensure the sync aggregate is valid if the block is accepted
+    spec.process_block(state, block)
+
+
+def _validator_index_for_pubkey(state, pubkey):
+    return list(map(lambda v: v.pubkey, state.validators)).index(pubkey)
+
+
+def _subnet_for_sync_committee_index(spec, i):
+    return i // (spec.SYNC_COMMITTEE_SIZE // spec.SYNC_COMMITTEE_SUBNET_COUNT)
+
+
+@with_all_phases_except([PHASE0])
+@with_state
+def test_compute_subnets_for_sync_committee(state, spec, phases):
+    some_sync_committee_members = list(
+        (
+            _subnet_for_sync_committee_index(spec, i),
+            pubkey,
+        )
+        for i, pubkey in enumerate(state.current_sync_committee.pubkeys)
+    )
+
+    expected_subnets_by_pubkey = defaultdict(list)
+    for (subnet, pubkey) in some_sync_committee_members:
+        expected_subnets_by_pubkey[pubkey].append(subnet)
+
+    for _, pubkey in some_sync_committee_members:
+        validator_index = _validator_index_for_pubkey(state, pubkey)
+        subnets = spec.compute_subnets_for_sync_committee(state, validator_index)
+        expected_subnets = expected_subnets_by_pubkey[pubkey]
+        assert subnets == expected_subnets