diff --git a/specs/altair/light-client/full-node.md b/specs/altair/light-client/full-node.md
index 53ba4dc82..2dd2ded6c 100644
--- a/specs/altair/light-client/full-node.md
+++ b/specs/altair/light-client/full-node.md
@@ -11,6 +11,7 @@
 - [Introduction](#introduction)
 - [Helper functions](#helper-functions)
   - [`compute_merkle_proof_for_state`](#compute_merkle_proof_for_state)
+  - [`block_to_light_client_header`](#block_to_light_client_header)
 - [Deriving light client data](#deriving-light-client-data)
   - [`create_light_client_bootstrap`](#create_light_client_bootstrap)
   - [`create_light_client_update`](#create_light_client_update)
@@ -34,6 +35,19 @@ def compute_merkle_proof_for_state(state: BeaconState,
     ...
 ```
 
+### `block_to_light_client_header`
+
+```python
+def block_to_light_client_header(block: SignedBeaconBlock) -> BeaconBlockHeader:
+    return BeaconBlockHeader(
+        slot=block.message.slot,
+        proposer_index=block.message.proposer_index,
+        parent_root=block.message.parent_root,
+        state_root=block.message.state_root,
+        body_root=hash_tree_root(block.message.body),
+    )
+```
+
 ## Deriving light client data
 
 Full nodes are expected to derive light client data from historic blocks and states and provide it to other clients.
@@ -55,13 +69,7 @@ def create_light_client_bootstrap(state: BeaconState,
     assert hash_tree_root(header) == hash_tree_root(block.message)
 
     return LightClientBootstrap(
-        header=BeaconBlockHeader(
-            slot=state.latest_block_header.slot,
-            proposer_index=state.latest_block_header.proposer_index,
-            parent_root=state.latest_block_header.parent_root,
-            state_root=hash_tree_root(state),
-            body_root=state.latest_block_header.body_root,
-        ),
+        header=block_to_light_client_header(block),
         current_sync_committee=state.current_sync_committee,
         current_sync_committee_branch=compute_merkle_proof_for_state(state, CURRENT_SYNC_COMMITTEE_INDEX),
     )
@@ -103,42 +111,30 @@ def create_light_client_update(state: BeaconState,
     assert hash_tree_root(attested_header) == hash_tree_root(attested_block.message) == block.message.parent_root
     update_attested_period = compute_sync_committee_period_at_slot(attested_block.message.slot)
 
+    update = LightClientUpdate()
+
+    update.attested_header = block_to_light_client_header(attested_block)
+
     # `next_sync_committee` is only useful if the message is signed by the current sync committee
     if update_attested_period == update_signature_period:
-        next_sync_committee = attested_state.next_sync_committee
-        next_sync_committee_branch = compute_merkle_proof_for_state(attested_state, NEXT_SYNC_COMMITTEE_INDEX)
-    else:
-        next_sync_committee = SyncCommittee()
-        next_sync_committee_branch = [Bytes32() for _ in range(floorlog2(NEXT_SYNC_COMMITTEE_INDEX))]
+        update.next_sync_committee = attested_state.next_sync_committee
+        update.next_sync_committee_branch = \
+            compute_merkle_proof_for_state(attested_state, NEXT_SYNC_COMMITTEE_INDEX)
 
     # Indicate finality whenever possible
     if finalized_block is not None:
         if finalized_block.message.slot != GENESIS_SLOT:
-            finalized_header = BeaconBlockHeader(
-                slot=finalized_block.message.slot,
-                proposer_index=finalized_block.message.proposer_index,
-                parent_root=finalized_block.message.parent_root,
-                state_root=finalized_block.message.state_root,
-                body_root=hash_tree_root(finalized_block.message.body),
-            )
-            assert hash_tree_root(finalized_header) == attested_state.finalized_checkpoint.root
+            update.finalized_header = block_to_light_client_header(finalized_block)
+            assert hash_tree_root(update.finalized_header) == attested_state.finalized_checkpoint.root
         else:
             assert attested_state.finalized_checkpoint.root == Bytes32()
-            finalized_header = BeaconBlockHeader()
-        finality_branch = compute_merkle_proof_for_state(attested_state, FINALIZED_ROOT_INDEX)
-    else:
-        finalized_header = BeaconBlockHeader()
-        finality_branch = [Bytes32() for _ in range(floorlog2(FINALIZED_ROOT_INDEX))]
+        update.finality_branch = \
+            compute_merkle_proof_for_state(attested_state, FINALIZED_ROOT_INDEX)
 
-    return LightClientUpdate(
-        attested_header=attested_header,
-        next_sync_committee=next_sync_committee,
-        next_sync_committee_branch=next_sync_committee_branch,
-        finalized_header=finalized_header,
-        finality_branch=finality_branch,
-        sync_aggregate=block.message.body.sync_aggregate,
-        signature_slot=block.message.slot,
-    )
+    update.sync_aggregate = block.message.body.sync_aggregate
+    update.signature_slot = block.message.slot
+
+    return update
 ```
 
 Full nodes SHOULD provide the best derivable `LightClientUpdate` (according to `is_better_update`) for each sync committee period covering any epochs in range `[max(ALTAIR_FORK_EPOCH, current_epoch - MIN_EPOCHS_FOR_BLOCK_REQUESTS), current_epoch]` where `current_epoch` is defined by the current wall-clock time. Full nodes MAY also provide `LightClientUpdate` for other sync committee periods.
diff --git a/tests/core/pyspec/eth2spec/test/altair/light_client/test_update_ranking.py b/tests/core/pyspec/eth2spec/test/altair/light_client/test_update_ranking.py
index 23ad79584..bde70a940 100644
--- a/tests/core/pyspec/eth2spec/test/altair/light_client/test_update_ranking.py
+++ b/tests/core/pyspec/eth2spec/test/altair/light_client/test_update_ranking.py
@@ -9,45 +9,23 @@ from eth2spec.test.helpers.attestations import (
 )
 from eth2spec.test.helpers.constants import MINIMAL
 from eth2spec.test.helpers.light_client import (
-    get_sync_aggregate,
-    signed_block_to_header,
+    create_update,
 )
 from eth2spec.test.helpers.state import (
     next_slots,
 )
-from math import floor
 
 
-def create_update(spec, test, with_next, with_finality, participation_rate):
+def create_test_update(spec, test, with_next, with_finality, participation_rate):
     attested_state, attested_block, finalized_block = test
-    num_participants = floor(spec.SYNC_COMMITTEE_SIZE * participation_rate)
-
-    attested_header = signed_block_to_header(spec, attested_block)
-
-    if with_next:
-        next_sync_committee = attested_state.next_sync_committee
-        next_sync_committee_branch = spec.compute_merkle_proof_for_state(attested_state, spec.NEXT_SYNC_COMMITTEE_INDEX)
-    else:
-        next_sync_committee = spec.SyncCommittee()
-        next_sync_committee_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.NEXT_SYNC_COMMITTEE_INDEX))]
-
-    if with_finality:
-        finalized_header = signed_block_to_header(spec, finalized_block)
-        finality_branch = spec.compute_merkle_proof_for_state(attested_state, spec.FINALIZED_ROOT_INDEX)
-    else:
-        finalized_header = spec.BeaconBlockHeader()
-        finality_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.FINALIZED_ROOT_INDEX))]
-
-    sync_aggregate, signature_slot = get_sync_aggregate(spec, attested_state, num_participants)
-
-    return spec.LightClientUpdate(
-        attested_header=attested_header,
-        next_sync_committee=next_sync_committee,
-        next_sync_committee_branch=next_sync_committee_branch,
-        finalized_header=finalized_header,
-        finality_branch=finality_branch,
-        sync_aggregate=sync_aggregate,
-        signature_slot=signature_slot,
+    return create_update(
+        spec,
+        attested_state,
+        attested_block,
+        finalized_block,
+        with_next,
+        with_finality,
+        participation_rate,
     )
 
 
@@ -84,76 +62,76 @@ def test_update_ranking(spec, state):
     # Create updates (in descending order of quality)
     updates = [
         # Updates with sync committee finality
-        create_update(spec, fin, with_next=1, with_finality=1, participation_rate=1.0),
-        create_update(spec, lat, with_next=1, with_finality=1, participation_rate=1.0),
-        create_update(spec, fin, with_next=1, with_finality=1, participation_rate=0.8),
-        create_update(spec, lat, with_next=1, with_finality=1, participation_rate=0.8),
+        create_test_update(spec, fin, with_next=1, with_finality=1, participation_rate=1.0),
+        create_test_update(spec, lat, with_next=1, with_finality=1, participation_rate=1.0),
+        create_test_update(spec, fin, with_next=1, with_finality=1, participation_rate=0.8),
+        create_test_update(spec, lat, with_next=1, with_finality=1, participation_rate=0.8),
 
         # Updates without sync committee finality
-        create_update(spec, att, with_next=1, with_finality=1, participation_rate=1.0),
-        create_update(spec, att, with_next=1, with_finality=1, participation_rate=0.8),
+        create_test_update(spec, att, with_next=1, with_finality=1, participation_rate=1.0),
+        create_test_update(spec, att, with_next=1, with_finality=1, participation_rate=0.8),
 
         # Updates without indication of any finality
-        create_update(spec, att, with_next=1, with_finality=0, participation_rate=1.0),
-        create_update(spec, fin, with_next=1, with_finality=0, participation_rate=1.0),
-        create_update(spec, lat, with_next=1, with_finality=0, participation_rate=1.0),
-        create_update(spec, att, with_next=1, with_finality=0, participation_rate=0.8),
-        create_update(spec, fin, with_next=1, with_finality=0, participation_rate=0.8),
-        create_update(spec, lat, with_next=1, with_finality=0, participation_rate=0.8),
+        create_test_update(spec, att, with_next=1, with_finality=0, participation_rate=1.0),
+        create_test_update(spec, fin, with_next=1, with_finality=0, participation_rate=1.0),
+        create_test_update(spec, lat, with_next=1, with_finality=0, participation_rate=1.0),
+        create_test_update(spec, att, with_next=1, with_finality=0, participation_rate=0.8),
+        create_test_update(spec, fin, with_next=1, with_finality=0, participation_rate=0.8),
+        create_test_update(spec, lat, with_next=1, with_finality=0, participation_rate=0.8),
 
         # Updates with sync committee finality but no `next_sync_committee`
-        create_update(spec, sig, with_next=0, with_finality=1, participation_rate=1.0),
-        create_update(spec, fin, with_next=0, with_finality=1, participation_rate=1.0),
-        create_update(spec, lat, with_next=0, with_finality=1, participation_rate=1.0),
-        create_update(spec, sig, with_next=0, with_finality=1, participation_rate=0.8),
-        create_update(spec, fin, with_next=0, with_finality=1, participation_rate=0.8),
-        create_update(spec, lat, with_next=0, with_finality=1, participation_rate=0.8),
+        create_test_update(spec, sig, with_next=0, with_finality=1, participation_rate=1.0),
+        create_test_update(spec, fin, with_next=0, with_finality=1, participation_rate=1.0),
+        create_test_update(spec, lat, with_next=0, with_finality=1, participation_rate=1.0),
+        create_test_update(spec, sig, with_next=0, with_finality=1, participation_rate=0.8),
+        create_test_update(spec, fin, with_next=0, with_finality=1, participation_rate=0.8),
+        create_test_update(spec, lat, with_next=0, with_finality=1, participation_rate=0.8),
 
         # Updates without sync committee finality and also no `next_sync_committee`
-        create_update(spec, att, with_next=0, with_finality=1, participation_rate=1.0),
-        create_update(spec, att, with_next=0, with_finality=1, participation_rate=0.8),
+        create_test_update(spec, att, with_next=0, with_finality=1, participation_rate=1.0),
+        create_test_update(spec, att, with_next=0, with_finality=1, participation_rate=0.8),
 
         # Updates without indication of any finality nor `next_sync_committee`
-        create_update(spec, sig, with_next=0, with_finality=0, participation_rate=1.0),
-        create_update(spec, att, with_next=0, with_finality=0, participation_rate=1.0),
-        create_update(spec, fin, with_next=0, with_finality=0, participation_rate=1.0),
-        create_update(spec, lat, with_next=0, with_finality=0, participation_rate=1.0),
-        create_update(spec, sig, with_next=0, with_finality=0, participation_rate=0.8),
-        create_update(spec, att, with_next=0, with_finality=0, participation_rate=0.8),
-        create_update(spec, fin, with_next=0, with_finality=0, participation_rate=0.8),
-        create_update(spec, lat, with_next=0, with_finality=0, participation_rate=0.8),
+        create_test_update(spec, sig, with_next=0, with_finality=0, participation_rate=1.0),
+        create_test_update(spec, att, with_next=0, with_finality=0, participation_rate=1.0),
+        create_test_update(spec, fin, with_next=0, with_finality=0, participation_rate=1.0),
+        create_test_update(spec, lat, with_next=0, with_finality=0, participation_rate=1.0),
+        create_test_update(spec, sig, with_next=0, with_finality=0, participation_rate=0.8),
+        create_test_update(spec, att, with_next=0, with_finality=0, participation_rate=0.8),
+        create_test_update(spec, fin, with_next=0, with_finality=0, participation_rate=0.8),
+        create_test_update(spec, lat, with_next=0, with_finality=0, participation_rate=0.8),
 
         # Updates with low sync committee participation
-        create_update(spec, fin, with_next=1, with_finality=1, participation_rate=0.4),
-        create_update(spec, lat, with_next=1, with_finality=1, participation_rate=0.4),
-        create_update(spec, att, with_next=1, with_finality=1, participation_rate=0.4),
-        create_update(spec, att, with_next=1, with_finality=0, participation_rate=0.4),
-        create_update(spec, fin, with_next=1, with_finality=0, participation_rate=0.4),
-        create_update(spec, lat, with_next=1, with_finality=0, participation_rate=0.4),
-        create_update(spec, sig, with_next=0, with_finality=1, participation_rate=0.4),
-        create_update(spec, fin, with_next=0, with_finality=1, participation_rate=0.4),
-        create_update(spec, lat, with_next=0, with_finality=1, participation_rate=0.4),
-        create_update(spec, att, with_next=0, with_finality=1, participation_rate=0.4),
-        create_update(spec, sig, with_next=0, with_finality=0, participation_rate=0.4),
-        create_update(spec, att, with_next=0, with_finality=0, participation_rate=0.4),
-        create_update(spec, fin, with_next=0, with_finality=0, participation_rate=0.4),
-        create_update(spec, lat, with_next=0, with_finality=0, participation_rate=0.4),
+        create_test_update(spec, fin, with_next=1, with_finality=1, participation_rate=0.4),
+        create_test_update(spec, lat, with_next=1, with_finality=1, participation_rate=0.4),
+        create_test_update(spec, att, with_next=1, with_finality=1, participation_rate=0.4),
+        create_test_update(spec, att, with_next=1, with_finality=0, participation_rate=0.4),
+        create_test_update(spec, fin, with_next=1, with_finality=0, participation_rate=0.4),
+        create_test_update(spec, lat, with_next=1, with_finality=0, participation_rate=0.4),
+        create_test_update(spec, sig, with_next=0, with_finality=1, participation_rate=0.4),
+        create_test_update(spec, fin, with_next=0, with_finality=1, participation_rate=0.4),
+        create_test_update(spec, lat, with_next=0, with_finality=1, participation_rate=0.4),
+        create_test_update(spec, att, with_next=0, with_finality=1, participation_rate=0.4),
+        create_test_update(spec, sig, with_next=0, with_finality=0, participation_rate=0.4),
+        create_test_update(spec, att, with_next=0, with_finality=0, participation_rate=0.4),
+        create_test_update(spec, fin, with_next=0, with_finality=0, participation_rate=0.4),
+        create_test_update(spec, lat, with_next=0, with_finality=0, participation_rate=0.4),
 
         # Updates with very low sync committee participation
-        create_update(spec, fin, with_next=1, with_finality=1, participation_rate=0.2),
-        create_update(spec, lat, with_next=1, with_finality=1, participation_rate=0.2),
-        create_update(spec, att, with_next=1, with_finality=1, participation_rate=0.2),
-        create_update(spec, att, with_next=1, with_finality=0, participation_rate=0.2),
-        create_update(spec, fin, with_next=1, with_finality=0, participation_rate=0.2),
-        create_update(spec, lat, with_next=1, with_finality=0, participation_rate=0.2),
-        create_update(spec, sig, with_next=0, with_finality=1, participation_rate=0.2),
-        create_update(spec, fin, with_next=0, with_finality=1, participation_rate=0.2),
-        create_update(spec, lat, with_next=0, with_finality=1, participation_rate=0.2),
-        create_update(spec, att, with_next=0, with_finality=1, participation_rate=0.2),
-        create_update(spec, sig, with_next=0, with_finality=0, participation_rate=0.2),
-        create_update(spec, att, with_next=0, with_finality=0, participation_rate=0.2),
-        create_update(spec, fin, with_next=0, with_finality=0, participation_rate=0.2),
-        create_update(spec, lat, with_next=0, with_finality=0, participation_rate=0.2),
+        create_test_update(spec, fin, with_next=1, with_finality=1, participation_rate=0.2),
+        create_test_update(spec, lat, with_next=1, with_finality=1, participation_rate=0.2),
+        create_test_update(spec, att, with_next=1, with_finality=1, participation_rate=0.2),
+        create_test_update(spec, att, with_next=1, with_finality=0, participation_rate=0.2),
+        create_test_update(spec, fin, with_next=1, with_finality=0, participation_rate=0.2),
+        create_test_update(spec, lat, with_next=1, with_finality=0, participation_rate=0.2),
+        create_test_update(spec, sig, with_next=0, with_finality=1, participation_rate=0.2),
+        create_test_update(spec, fin, with_next=0, with_finality=1, participation_rate=0.2),
+        create_test_update(spec, lat, with_next=0, with_finality=1, participation_rate=0.2),
+        create_test_update(spec, att, with_next=0, with_finality=1, participation_rate=0.2),
+        create_test_update(spec, sig, with_next=0, with_finality=0, participation_rate=0.2),
+        create_test_update(spec, att, with_next=0, with_finality=0, participation_rate=0.2),
+        create_test_update(spec, fin, with_next=0, with_finality=0, participation_rate=0.2),
+        create_test_update(spec, lat, with_next=0, with_finality=0, participation_rate=0.2),
     ]
     yield "updates", updates
 
diff --git a/tests/core/pyspec/eth2spec/test/altair/unittests/light_client/test_sync_protocol.py b/tests/core/pyspec/eth2spec/test/altair/unittests/light_client/test_sync_protocol.py
index bf09cc30e..a72f1980b 100644
--- a/tests/core/pyspec/eth2spec/test/altair/unittests/light_client/test_sync_protocol.py
+++ b/tests/core/pyspec/eth2spec/test/altair/unittests/light_client/test_sync_protocol.py
@@ -11,43 +11,44 @@ from eth2spec.test.helpers.attestations import (
 )
 from eth2spec.test.helpers.constants import MINIMAL
 from eth2spec.test.helpers.light_client import (
-    get_sync_aggregate,
-    initialize_light_client_store,
-    signed_block_to_header,
+    create_update,
 )
 from eth2spec.test.helpers.state import (
     next_slots,
 )
 
 
+def setup_test(spec, state):
+    trusted_block = spec.SignedBeaconBlock()
+    trusted_block.message.state_root = state.hash_tree_root()
+    trusted_block_root = trusted_block.message.hash_tree_root()
+    bootstrap = spec.create_light_client_bootstrap(state, trusted_block)
+    store = spec.initialize_light_client_store(trusted_block_root, bootstrap)
+    store.next_sync_committee = state.next_sync_committee
+
+    return (trusted_block, store)
+
+
 @with_altair_and_later
 @spec_state_test_with_matching_config
 def test_process_light_client_update_not_timeout(spec, state):
-    store = initialize_light_client_store(spec, state)
+    genesis_block, store = setup_test(spec, state)
 
     # Block at slot 1 doesn't increase sync committee period, so it won't force update store.finalized_header
     attested_block = state_transition_with_full_block(spec, state, False, False)
-    attested_header = signed_block_to_header(spec, attested_block)
-
-    # Sync committee signing the attested_header
-    sync_aggregate, signature_slot = get_sync_aggregate(spec, state)
-    next_sync_committee = spec.SyncCommittee()
-    next_sync_committee_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.NEXT_SYNC_COMMITTEE_INDEX))]
+    signature_slot = state.slot + 1
 
     # Ensure that finality checkpoint is genesis
     assert state.finalized_checkpoint.epoch == 0
-    # Finality is unchanged
-    finalized_header = spec.BeaconBlockHeader()
-    finality_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.FINALIZED_ROOT_INDEX))]
 
-    update = spec.LightClientUpdate(
-        attested_header=attested_header,
-        next_sync_committee=next_sync_committee,
-        next_sync_committee_branch=next_sync_committee_branch,
-        finalized_header=finalized_header,
-        finality_branch=finality_branch,
-        sync_aggregate=sync_aggregate,
-        signature_slot=signature_slot,
+    update = create_update(
+        spec,
+        attested_state=state,
+        attested_block=attested_block,
+        finalized_block=genesis_block,
+        with_next=False,
+        with_finality=False,
+        participation_rate=1.0,
     )
 
     pre_store = deepcopy(store)
@@ -64,7 +65,7 @@ def test_process_light_client_update_not_timeout(spec, state):
 @spec_state_test_with_matching_config
 @with_presets([MINIMAL], reason="too slow")
 def test_process_light_client_update_at_period_boundary(spec, state):
-    store = initialize_light_client_store(spec, state)
+    genesis_block, store = setup_test(spec, state)
 
     # Forward to slot before next sync committee period so that next block is final one in period
     next_slots(spec, state, spec.UPDATE_TIMEOUT - 2)
@@ -73,25 +74,16 @@ def test_process_light_client_update_at_period_boundary(spec, state):
     assert store_period == update_period
 
     attested_block = state_transition_with_full_block(spec, state, False, False)
-    attested_header = signed_block_to_header(spec, attested_block)
+    signature_slot = state.slot + 1
 
-    # Sync committee signing the attested_header
-    sync_aggregate, signature_slot = get_sync_aggregate(spec, state)
-    next_sync_committee = spec.SyncCommittee()
-    next_sync_committee_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.NEXT_SYNC_COMMITTEE_INDEX))]
-
-    # Finality is unchanged
-    finalized_header = spec.BeaconBlockHeader()
-    finality_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.FINALIZED_ROOT_INDEX))]
-
-    update = spec.LightClientUpdate(
-        attested_header=attested_header,
-        next_sync_committee=next_sync_committee,
-        next_sync_committee_branch=next_sync_committee_branch,
-        finalized_header=finalized_header,
-        finality_branch=finality_branch,
-        sync_aggregate=sync_aggregate,
-        signature_slot=signature_slot,
+    update = create_update(
+        spec,
+        attested_state=state,
+        attested_block=attested_block,
+        finalized_block=genesis_block,
+        with_next=False,
+        with_finality=False,
+        participation_rate=1.0,
     )
 
     pre_store = deepcopy(store)
@@ -108,7 +100,7 @@ def test_process_light_client_update_at_period_boundary(spec, state):
 @spec_state_test_with_matching_config
 @with_presets([MINIMAL], reason="too slow")
 def test_process_light_client_update_timeout(spec, state):
-    store = initialize_light_client_store(spec, state)
+    genesis_block, store = setup_test(spec, state)
 
     # Forward to next sync committee period
     next_slots(spec, state, spec.UPDATE_TIMEOUT)
@@ -117,26 +109,16 @@ def test_process_light_client_update_timeout(spec, state):
     assert store_period + 1 == update_period
 
     attested_block = state_transition_with_full_block(spec, state, False, False)
-    attested_header = signed_block_to_header(spec, attested_block)
+    signature_slot = state.slot + 1
 
-    # Sync committee signing the attested_header
-    sync_aggregate, signature_slot = get_sync_aggregate(spec, state)
-
-    # Sync committee is updated
-    next_sync_committee = state.next_sync_committee
-    next_sync_committee_branch = spec.compute_merkle_proof_for_state(state, spec.NEXT_SYNC_COMMITTEE_INDEX)
-    # Finality is unchanged
-    finalized_header = spec.BeaconBlockHeader()
-    finality_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.FINALIZED_ROOT_INDEX))]
-
-    update = spec.LightClientUpdate(
-        attested_header=attested_header,
-        next_sync_committee=next_sync_committee,
-        next_sync_committee_branch=next_sync_committee_branch,
-        finalized_header=finalized_header,
-        finality_branch=finality_branch,
-        sync_aggregate=sync_aggregate,
-        signature_slot=signature_slot,
+    update = create_update(
+        spec,
+        attested_state=state,
+        attested_block=attested_block,
+        finalized_block=genesis_block,
+        with_next=True,
+        with_finality=False,
+        participation_rate=1.0,
     )
 
     pre_store = deepcopy(store)
@@ -153,7 +135,7 @@ def test_process_light_client_update_timeout(spec, state):
 @spec_state_test_with_matching_config
 @with_presets([MINIMAL], reason="too slow")
 def test_process_light_client_update_finality_updated(spec, state):
-    store = initialize_light_client_store(spec, state)
+    _, store = setup_test(spec, state)
 
     # Change finality
     blocks = []
@@ -169,28 +151,21 @@ def test_process_light_client_update_finality_updated(spec, state):
     assert store_period == update_period
 
     attested_block = blocks[-1]
-    attested_header = signed_block_to_header(spec, attested_block)
+    signature_slot = state.slot + 1
 
-    # Sync committee signing the attested_header
-    sync_aggregate, signature_slot = get_sync_aggregate(spec, state)
-
-    # Updated sync_committee and finality
-    next_sync_committee = spec.SyncCommittee()
-    next_sync_committee_branch = [spec.Bytes32() for _ in range(spec.floorlog2(spec.NEXT_SYNC_COMMITTEE_INDEX))]
+    # Updated finality
     finalized_block = blocks[spec.SLOTS_PER_EPOCH - 1]
-    finalized_header = signed_block_to_header(spec, finalized_block)
-    assert finalized_header.slot == spec.compute_start_slot_at_epoch(state.finalized_checkpoint.epoch)
-    assert finalized_header.hash_tree_root() == state.finalized_checkpoint.root
-    finality_branch = spec.compute_merkle_proof_for_state(state, spec.FINALIZED_ROOT_INDEX)
+    assert finalized_block.message.slot == spec.compute_start_slot_at_epoch(state.finalized_checkpoint.epoch)
+    assert finalized_block.message.hash_tree_root() == state.finalized_checkpoint.root
 
-    update = spec.LightClientUpdate(
-        attested_header=attested_header,
-        next_sync_committee=next_sync_committee,
-        next_sync_committee_branch=next_sync_committee_branch,
-        finalized_header=finalized_header,
-        finality_branch=finality_branch,
-        sync_aggregate=sync_aggregate,
-        signature_slot=signature_slot,
+    update = create_update(
+        spec,
+        attested_state=state,
+        attested_block=attested_block,
+        finalized_block=finalized_block,
+        with_next=False,
+        with_finality=True,
+        participation_rate=1.0,
     )
 
     spec.process_light_client_update(store, update, signature_slot, state.genesis_validators_root)
diff --git a/tests/core/pyspec/eth2spec/test/helpers/light_client.py b/tests/core/pyspec/eth2spec/test/helpers/light_client.py
index 8d632b3a1..39175a352 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/light_client.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/light_client.py
@@ -5,28 +5,7 @@ from eth2spec.test.helpers.sync_committee import (
     compute_aggregate_sync_committee_signature,
     compute_committee_indices,
 )
-
-
-def signed_block_to_header(spec, block):
-    return spec.BeaconBlockHeader(
-        slot=block.message.slot,
-        proposer_index=block.message.proposer_index,
-        parent_root=block.message.parent_root,
-        state_root=block.message.state_root,
-        body_root=block.message.body.hash_tree_root(),
-    )
-
-
-def initialize_light_client_store(spec, state):
-    return spec.LightClientStore(
-        finalized_header=spec.BeaconBlockHeader(),
-        current_sync_committee=state.current_sync_committee,
-        next_sync_committee=state.next_sync_committee,
-        best_valid_update=None,
-        optimistic_header=spec.BeaconBlockHeader(),
-        previous_max_active_participants=0,
-        current_max_active_participants=0,
-    )
+from math import floor
 
 
 def get_sync_aggregate(spec, state, num_participants=None, signature_slot=None):
@@ -60,3 +39,32 @@ def get_sync_aggregate(spec, state, num_participants=None, signature_slot=None):
         sync_committee_signature=sync_committee_signature,
     )
     return sync_aggregate, signature_slot
+
+
+def create_update(spec,
+                  attested_state,
+                  attested_block,
+                  finalized_block,
+                  with_next,
+                  with_finality,
+                  participation_rate):
+    num_participants = floor(spec.SYNC_COMMITTEE_SIZE * participation_rate)
+
+    update = spec.LightClientUpdate()
+
+    update.attested_header = spec.block_to_light_client_header(attested_block)
+
+    if with_next:
+        update.next_sync_committee = attested_state.next_sync_committee
+        update.next_sync_committee_branch = \
+            spec.compute_merkle_proof_for_state(attested_state, spec.NEXT_SYNC_COMMITTEE_INDEX)
+
+    if with_finality:
+        update.finalized_header = spec.block_to_light_client_header(finalized_block)
+        update.finality_branch = \
+            spec.compute_merkle_proof_for_state(attested_state, spec.FINALIZED_ROOT_INDEX)
+
+    update.sync_aggregate, update.signature_slot = \
+        get_sync_aggregate(spec, attested_state, num_participants)
+
+    return update