add some attestation tests. fix genesi crosslink bug

specs/core/0_beacon-chain.md

@@ -905,21 +905,20 @@ def get_crosslink_committees_at_slot(state: BeaconState,
     next_epoch = current_epoch + 1
 
     assert previous_epoch <= epoch <= next_epoch
-    active_validator_indices = get_active_validator_indices(
+    indices = get_active_validator_indices(
         state.validator_registry,
         epoch,
     )
-    committees_per_epoch = get_epoch_committee_count(len(active_validator_indices))
+    committees_per_epoch = get_epoch_committee_count(len(indices))
 
     if epoch == current_epoch:
         start_shard = state.latest_start_shard
     elif epoch == previous_epoch:
-        start_shard = (state.latest_start_shard - SLOTS_PER_EPOCH * committees_per_epoch) % SHARD_COUNT
+        start_shard = (state.latest_start_shard - committees_per_epoch) % SHARD_COUNT
     elif epoch == next_epoch:
         current_epoch_committees = get_current_epoch_committee_count(state)
-        start_shard = (state.latest_start_shard + EPOCH_LENGTH * current_epoch_committees) % SHARD_COUNT
+        start_shard = (state.latest_start_shard + current_epoch_committees) % SHARD_COUNT
 
-    indices = get_active_validator_indices(state.validator_registry, epoch)
     committees_per_slot = committees_per_epoch // SLOTS_PER_EPOCH
     offset = slot % SLOTS_PER_EPOCH
     slot_start_shard = (start_shard + committees_per_slot * offset) % SHARD_COUNT
@@ -1830,7 +1829,7 @@ Run the following function:
 ```python
 def process_crosslinks(state: BeaconState) -> None:
     current_epoch = get_current_epoch(state)
-    previous_epoch = current_epoch - 1
+    previous_epoch = max(current_epoch - 1, GENESIS_EPOCH)
     next_epoch = current_epoch + 1
     for slot in range(get_epoch_start_slot(previous_epoch), get_epoch_start_slot(next_epoch)):
         for crosslink_committee, shard in get_crosslink_committees_at_slot(state, slot):

tests/phase0/block_processing/test_process_attestation.py

@@ -0,0 +1,67 @@
+from copy import deepcopy
+import pytest
+
+import build.phase0.spec as spec
+
+from build.phase0.state_transition import (
+    state_transition,
+)
+from build.phase0.spec import (
+    ZERO_HASH,
+    get_current_epoch,
+    process_attestation,
+    slot_to_epoch,
+)
+from tests.phase0.helpers import (
+    build_empty_block_for_next_slot,
+    get_valid_attestation,
+)
+
+
+# mark entire file as 'attestations'
+pytestmark = pytest.mark.attestations
+
+
+def run_attestation_processing(state, attestation, valid=True):
+    """
+    Run ``process_attestation`` returning the pre and post state.
+    If ``valid == False``, run expecting ``AssertionError``
+    """
+    post_state = deepcopy(state)
+
+    if not valid:
+        with pytest.raises(AssertionError):
+            process_attestation(post_state, attestation)
+        return state, None
+
+    process_attestation(post_state, attestation)
+
+    current_epoch = get_current_epoch(state)
+    target_epoch = slot_to_epoch(attestation.data.slot)
+    if target_epoch == current_epoch:
+        assert len(post_state.current_epoch_attestations) == len(state.current_epoch_attestations) + 1
+    else:
+        assert len(post_state.previous_epoch_attestations) == len(state.previous_epoch_attestations) + 1
+
+
+    return state, post_state
+
+
+def test_success(state):
+    attestation = get_valid_attestation(state)
+    state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
+
+    pre_state, post_state = run_attestation_processing(state, attestation)
+
+    return pre_state, attestation, post_state
+
+
+def test_success_prevous_epoch(state):
+    attestation = get_valid_attestation(state)
+    block = build_empty_block_for_next_slot(state)
+    block.slot = state.slot + spec.SLOTS_PER_EPOCH
+    state_transition(state, block)
+
+    pre_state, post_state = run_attestation_processing(state, attestation)
+
+    return pre_state, attestation, post_state

tests/phase0/helpers.py

@@ -9,7 +9,9 @@ from build.phase0.spec import (
     EMPTY_SIGNATURE,
     ZERO_HASH,
     # SSZ
+    Attestation,
     AttestationData,
+    AttestationDataAndCustodyBit,
     BeaconBlockHeader,
     Deposit,
     DepositData,
@@ -18,7 +20,9 @@ from build.phase0.spec import (
     VoluntaryExit,
     # functions
     get_active_validator_indices,
+    get_attestation_participants,
     get_block_root,
+    get_crosslink_committees_at_slot,
     get_current_epoch,
     get_domain,
     get_empty_block,
@@ -236,3 +240,49 @@ def get_valid_proposer_slashing(state):
         header_1=header_1,
         header_2=header_2,
     )
+
+
+def get_valid_attestation(state, slot=None):
+    if slot is None:
+        slot = state.slot
+    shard = state.latest_start_shard
+    attestation_data = build_attestation_data(state, slot, shard)
+
+    crosslink_committees = get_crosslink_committees_at_slot(state, slot)
+    crosslink_committee = [committee for committee, _shard in crosslink_committees if _shard == attestation_data.shard][0]
+
+    committee_size = len(crosslink_committee)
+    bitfield_length = (committee_size + 7) // 8
+    aggregation_bitfield = b'\x01' + b'\x00' * (bitfield_length - 1)
+    custody_bitfield = b'\x00' * bitfield_length
+    attestation = Attestation(
+        aggregation_bitfield=aggregation_bitfield,
+        data=attestation_data,
+        custody_bitfield=custody_bitfield,
+        aggregate_signature=EMPTY_SIGNATURE,
+    )
+    participants = get_attestation_participants(
+        state,
+        attestation.data,
+        attestation.aggregation_bitfield,
+    )
+    assert len(participants) == 1
+
+    validator_index = participants[0]
+    privkey = privkeys[validator_index]
+
+    message_hash = AttestationDataAndCustodyBit(
+        data=attestation.data,
+        custody_bit=0b0,
+    ).hash_tree_root()
+
+    attestation.aggregation_signature = bls.sign(
+        message_hash=message_hash,
+        privkey=privkey,
+        domain=get_domain(
+            fork=state.fork,
+            epoch=get_current_epoch(state),
+            domain_type=spec.DOMAIN_ATTESTATION,
+        )
+    )
+    return attestation

tests/phase0/test_sanity.py

@@ -11,19 +11,13 @@ from build.phase0.spec import (
     EMPTY_SIGNATURE,
     ZERO_HASH,
     # SSZ
-    Attestation,
-    AttestationDataAndCustodyBit,
-    BeaconBlockHeader,
     Deposit,
     Transfer,
-    ProposerSlashing,
     VoluntaryExit,
     # functions
     get_active_validator_indices,
-    get_attestation_participants,
     get_balance,
     get_block_root,
-    get_crosslink_committees_at_slot,
     get_current_epoch,
     get_domain,
     get_state_root,
@@ -42,10 +36,10 @@ from build.phase0.utils.merkle_minimal import (
     get_merkle_root,
 )
 from tests.phase0.helpers import (
-    build_attestation_data,
     build_deposit_data,
     build_empty_block_for_next_slot,
     force_registry_change_at_next_epoch,
+    get_valid_attestation,
     get_valid_proposer_slashing,
     privkeys,
     pubkeys,
@@ -222,47 +216,7 @@ def test_deposit_top_up(state):
 
 def test_attestation(state):
     test_state = deepcopy(state)
-    slot = state.slot
+    attestation = get_valid_attestation(state)
-    shard = state.latest_start_shard
-    attestation_data = build_attestation_data(state, slot, shard)
-
-    crosslink_committees = get_crosslink_committees_at_slot(state, slot)
-    crosslink_committee = [committee for committee, _shard in crosslink_committees if _shard == attestation_data.shard][0]
-
-    committee_size = len(crosslink_committee)
-    bitfield_length = (committee_size + 7) // 8
-    aggregation_bitfield = b'\x01' + b'\x00' * (bitfield_length - 1)
-    custody_bitfield = b'\x00' * bitfield_length
-    attestation = Attestation(
-        aggregation_bitfield=aggregation_bitfield,
-        data=attestation_data,
-        custody_bitfield=custody_bitfield,
-        aggregate_signature=EMPTY_SIGNATURE,
-    )
-    participants = get_attestation_participants(
-        test_state,
-        attestation.data,
-        attestation.aggregation_bitfield,
-    )
-    assert len(participants) == 1
-
-    validator_index = participants[0]
-    privkey = privkeys[validator_index]
-
-    message_hash = AttestationDataAndCustodyBit(
-        data=attestation.data,
-        custody_bit=0b0,
-    ).hash_tree_root()
-
-    attestation.aggregation_signature = bls.sign(
-        message_hash=message_hash,
-        privkey=privkey,
-        domain=get_domain(
-            fork=test_state.fork,
-            epoch=get_current_epoch(test_state),
-            domain_type=spec.DOMAIN_ATTESTATION,
-        )
-    )
 
     #
     # Add to state via block transition