diff --git a/tests/core/pyspec/eth2spec/test/helpers/attestations.py b/tests/core/pyspec/eth2spec/test/helpers/attestations.py
index 377426006..85b543104 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/attestations.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/attestations.py
@@ -113,8 +113,8 @@ def get_valid_late_attestation(spec, state, slot=None, index=None, signed=False)
     return get_valid_attestation(spec, state, slot=slot, index=index, signed=signed, on_time=False)
 
 
-def get_valid_attestation(spec, state, slot=None, index=None, empty=False, signed=False, on_time=True):
-    # If empty is true, the attestation has 0 participants, and will not be signed.
+def get_valid_attestation(spec, state, slot=None, index=None, filter_participant_set=None, signed=False, on_time=True):
+    # If filter_participant_set is filters everything, the attestation has 0 participants, and cannot be signed.
     # Thus strictly speaking invalid when no participant is added later.
 
     if slot is None:
@@ -136,10 +136,8 @@ def get_valid_attestation(spec, state, slot=None, index=None, empty=False, signe
         aggregation_bits=aggregation_bits,
         data=attestation_data,
     )
-    if not empty:
-        fill_aggregate_attestation(spec, state, attestation)
-    if signed:
-        sign_attestation(spec, state, attestation)
+    # fill the attestation with (optionally filtered) participants, and optionally sign it
+    fill_aggregate_attestation(spec, state, attestation, signed=signed, filter_participant_set=filter_participant_set)
 
     if spec.fork == 'phase1' and on_time:
         attestation = convert_to_valid_on_time_attestation(spec, state, attestation, signed)
@@ -232,16 +230,25 @@ def get_attestation_signature(spec, state, attestation_data, privkey):
     return bls.Sign(privkey, signing_root)
 
 
-def fill_aggregate_attestation(spec, state, attestation, signed=False):
+def fill_aggregate_attestation(spec, state, attestation, signed=False, filter_participant_set=None):
+    """
+     `signed`: Signing is optional.
+     `filter_participant_set`: Optional, filters the full committee indices set (default) to a subset that participates
+    """
     beacon_committee = spec.get_beacon_committee(
         state,
         attestation.data.slot,
         attestation.data.index,
     )
+    # By default, have everyone participate
+    participants = set(beacon_committee)
+    # But optionally filter the participants to a smaller amount
+    if filter_participant_set is not None:
+        participants = filter_participant_set(participants)
     for i in range(len(beacon_committee)):
-        attestation.aggregation_bits[i] = True
+        attestation.aggregation_bits[i] = beacon_committee[i] in participants
 
-    if signed:
+    if signed and len(participants) > 0:
         sign_attestation(spec, state, attestation)
 
 
diff --git a/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py b/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py
index df3279faa..bb25a384e 100644
--- a/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py
+++ b/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py
@@ -13,7 +13,6 @@ from eth2spec.test.helpers.attestations import (
     sign_attestation,
 )
 from eth2spec.test.helpers.state import (
-    next_slot,
     next_slots,
     next_epoch,
     transition_to,
@@ -68,7 +67,7 @@ def test_invalid_attestation_signature(spec, state):
 @spec_state_test
 @always_bls
 def test_empty_participants_zeroes_sig(spec, state):
-    attestation = get_valid_attestation(spec, state, empty=True)
+    attestation = get_valid_attestation(spec, state, filter_participant_set=lambda comm: [])  # 0 participants
     attestation.signature = spec.BLSSignature(b'\x00' * 96)
     next_slots(spec, state, spec.MIN_ATTESTATION_INCLUSION_DELAY)
 
@@ -79,7 +78,7 @@ def test_empty_participants_zeroes_sig(spec, state):
 @spec_state_test
 @always_bls
 def test_empty_participants_seemingly_valid_sig(spec, state):
-    attestation = get_valid_attestation(spec, state, empty=True)
+    attestation = get_valid_attestation(spec, state, filter_participant_set=lambda comm: [])  # 0 participants
     # Special BLS value, valid for zero pubkeys on some (but not all) BLS implementations.
     attestation.signature = spec.BLSSignature(b'\xc0' + b'\x00' * 95)
     next_slots(spec, state, spec.MIN_ATTESTATION_INCLUSION_DELAY)
@@ -283,19 +282,6 @@ def test_bad_source_root(spec, state):
     yield from run_attestation_processing(spec, state, attestation, False)
 
 
-@with_all_phases
-@spec_state_test
-def test_empty_aggregation_bits(spec, state):
-    next_slot(spec, state)
-    attestation = get_valid_attestation(spec, state, empty=True)
-    next_slots(spec, state, spec.MIN_ATTESTATION_INCLUSION_DELAY)
-
-    assert attestation.aggregation_bits == Bitlist[spec.MAX_VALIDATORS_PER_COMMITTEE](
-        *([0b0] * len(attestation.aggregation_bits)))
-
-    yield from run_attestation_processing(spec, state, attestation)
-
-
 @with_all_phases
 @spec_state_test
 def test_too_many_aggregation_bits(spec, state):
diff --git a/tests/core/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_rewards_and_penalties.py b/tests/core/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_rewards_and_penalties.py
index b862b5c48..63aafe521 100644
--- a/tests/core/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_rewards_and_penalties.py
+++ b/tests/core/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_rewards_and_penalties.py
@@ -15,15 +15,15 @@ from eth2spec.test.helpers.attestations import (
 )
 from eth2spec.test.helpers.attester_slashings import get_indexed_attestation_participants
 from eth2spec.test.phase_0.epoch_processing.run_epoch_process_base import run_epoch_processing_with
+from random import Random
 
 
 def run_process_rewards_and_penalties(spec, state):
     yield from run_epoch_processing_with(spec, state, 'process_rewards_and_penalties')
 
 
-def prepare_state_with_full_attestations(spec, state, empty=False):
-    # If empty is true, attestations have 0 participants, and are not signed.
-    # Thus strictly speaking invalid when no participant is added later.
+def prepare_state_with_full_attestations(spec, state, participation_fn=None):
+    # participation_fn: (slot, committee_index, committee_indices_set) -> participants_indices_set
 
     # Go to start of next epoch to ensure can have full participation
     next_epoch(spec, state)
@@ -36,8 +36,15 @@ def prepare_state_with_full_attestations(spec, state, empty=False):
         # create an attestation for each index in each slot in epoch
         if state.slot < next_epoch_start_slot:
             for committee_index in range(spec.get_committee_count_at_slot(state, state.slot)):
-                attestation = get_valid_attestation(spec, state, index=committee_index, empty=empty, signed=True)
-                attestations.append(attestation)
+                def temp_participants_filter(comm):
+                    if participation_fn is None:
+                        return comm
+                    else:
+                        return participation_fn(state.slot, committee_index, comm)
+                attestation = get_valid_attestation(spec, state, index=committee_index,
+                                                    filter_participant_set=temp_participants_filter, signed=True)
+                if any(attestation.aggregation_bits):  # Only if there is at least 1 participant.
+                    attestations.append(attestation)
         # fill each created slot in state after inclusion delay
         if state.slot >= start_slot + spec.MIN_ATTESTATION_INCLUSION_DELAY:
             inclusion_slot = state.slot - spec.MIN_ATTESTATION_INCLUSION_DELAY
@@ -192,20 +199,55 @@ def test_no_attestations_all_penalties(spec, state):
         assert state.balances[index] < pre_state.balances[index]
 
 
-@with_all_phases
-@spec_state_test
-def test_empty_attestations(spec, state):
-    attestations = prepare_state_with_full_attestations(spec, state, empty=True)
+def run_with_participation(spec, state, participation_fn):
+    participated = set()
+
+    def participation_tracker(slot, comm_index, comm):
+        att_participants = participation_fn(slot, comm_index, comm)
+        participated.update(att_participants)
+        return att_participants
+
+    attestations = prepare_state_with_full_attestations(spec, state, participation_fn=participation_tracker)
 
     pre_state = state.copy()
 
     yield from run_process_rewards_and_penalties(spec, state)
 
     attesting_indices = spec.get_unslashed_attesting_indices(state, attestations)
-    assert len(attesting_indices) == 0
+    assert len(attesting_indices) == len(participated)
 
     for index in range(len(pre_state.validators)):
-        assert state.balances[index] < pre_state.balances[index]
+        if index in participated:
+            assert state.balances[index] > pre_state.balances[index]
+        else:
+            assert state.balances[index] < pre_state.balances[index]
+
+
+@with_all_phases
+@spec_state_test
+def test_almost_empty_attestations(spec, state):
+    rng = Random(1234)
+    yield from run_with_participation(spec, state, lambda slot, comm_index, comm: rng.sample(comm, 1))
+
+
+@with_all_phases
+@spec_state_test
+def test_random_fill_attestations(spec, state):
+    rng = Random(4567)
+    yield from run_with_participation(spec, state, lambda slot, comm_index, comm: rng.sample(comm, len(comm) // 3))
+
+
+@with_all_phases
+@spec_state_test
+def test_almost_full_attestations(spec, state):
+    rng = Random(8901)
+    yield from run_with_participation(spec, state, lambda slot, comm_index, comm: rng.sample(comm, len(comm) - 1))
+
+
+@with_all_phases
+@spec_state_test
+def test_full_attestation_participation(spec, state):
+    yield from run_with_participation(spec, state, lambda slot, comm_index, comm: comm)
 
 
 @with_all_phases