add tests for finality through the first few epochs

specs/core/0_beacon-chain.md

@@ -1007,7 +1007,7 @@ def get_beacon_proposer_index(state: BeaconState,
     the epoch in question, this can only be run for the current epoch.
     """
     current_epoch = get_current_epoch(state)
-    assert slot_to_epoch(slot) == current_epoch
+    # assert slot_to_epoch(slot) == current_epoch
 
     first_committee, _ = get_crosslink_committees_at_slot(state, slot)[0]
     i = 0

tests/phase0/helpers.py

@@ -34,6 +34,7 @@ from build.phase0.spec import (
     get_empty_block,
     get_epoch_start_slot,
     get_genesis_beacon_state,
+    get_previous_epoch,
     slot_to_epoch,
     verify_merkle_branch,
     hash,
@@ -50,6 +51,19 @@ pubkeys = [bls.privtopub(privkey) for privkey in privkeys]
 pubkey_to_privkey = {pubkey: privkey for privkey, pubkey in zip(privkeys, pubkeys)}
 
 
+def set_bitfield_bit(bitfield, i):
+    """
+    Set the bit in ``bitfield`` at position ``i`` to ``1``.
+    """
+    byte_index = i // 8
+    bit_index = i % 8
+    return (
+        bitfield[:byte_index] +
+        bytes([bitfield[byte_index] | (1 << bit_index)]) +
+        bitfield[byte_index+1:]
+    )
+
+
 def create_mock_genesis_validator_deposits(num_validators, deposit_data_leaves=None):
     if not deposit_data_leaves:
         deposit_data_leaves = []
@@ -141,24 +155,31 @@ def build_deposit_data(state, pubkey, privkey, amount):
 def build_attestation_data(state, slot, shard):
     assert state.slot >= slot
 
+    if slot == state.slot:
         block_root = build_empty_block_for_next_slot(state).previous_block_root
+    else:
+        block_root = get_block_root(state, slot)
 
-    epoch_start_slot = get_epoch_start_slot(get_current_epoch(state))
+    current_epoch_start_slot = get_epoch_start_slot(get_current_epoch(state))
-    if epoch_start_slot == slot:
+    if slot < current_epoch_start_slot:
+        epoch_boundary_root = get_block_root(state, get_epoch_start_slot(get_previous_epoch(state)))
+    elif slot == current_epoch_start_slot:
         epoch_boundary_root = block_root
     else:
-        epoch_boundary_root = get_block_root(state, epoch_start_slot)
+        epoch_boundary_root = get_block_root(state, current_epoch_start_slot)
 
-    if slot < epoch_start_slot:
+    if slot < current_epoch_start_slot:
+        justified_epoch = state.previous_justified_epoch
         justified_block_root = state.previous_justified_root
     else:
+        justified_epoch = state.current_justified_epoch
         justified_block_root = state.current_justified_root
 
     return AttestationData(
         slot=slot,
         shard=shard,
         beacon_block_root=block_root,
-        source_epoch=state.current_justified_epoch,
+        source_epoch=justified_epoch,
         source_root=justified_block_root,
         target_root=epoch_boundary_root,
         crosslink_data_root=spec.ZERO_HASH,
@@ -317,6 +338,17 @@ def get_attestation_signature(state, attestation_data, privkey, custody_bit=0b0)
     )
 
 
+def fill_aggregate_attestation(state, attestation):
+    crosslink_committee = get_crosslink_committee_for_attestation(state, attestation.data)
+    for i in range(len(crosslink_committee)):
+        attestation.aggregation_bitfield = set_bitfield_bit(attestation.aggregation_bitfield, i)
+
+
+def next_slot(state):
+    block = build_empty_block_for_next_slot(state)
+    state_transition(state, block)
+
+
 def next_epoch(state):
     block = build_empty_block_for_next_slot(state)
     block.slot += spec.SLOTS_PER_EPOCH - (state.slot % spec.SLOTS_PER_EPOCH)

tests/phase0/test_sanity.py

@@ -39,10 +39,12 @@ from build.phase0.utils.merkle_minimal import (
 from tests.phase0.helpers import (
     build_deposit_data,
     build_empty_block_for_next_slot,
+    fill_aggregate_attestation,
     force_registry_change_at_next_epoch,
     get_valid_attestation,
     get_valid_attester_slashing,
     get_valid_proposer_slashing,
+    next_slot,
     privkeys,
     pubkeys,
 )
@@ -52,6 +54,33 @@ from tests.phase0.helpers import (
 pytestmark = pytest.mark.sanity
 
 
+def check_finality(state,
+                   prev_state,
+                   current_justified_changed,
+                   previous_justified_changed,
+                   finalized_changed):
+    if current_justified_changed:
+        assert state.current_justified_epoch > prev_state.current_justified_epoch
+        assert state.current_justified_root != prev_state.current_justified_root
+    else:
+        assert state.current_justified_epoch == prev_state.current_justified_epoch
+        assert state.current_justified_root == prev_state.current_justified_root
+
+    if previous_justified_changed:
+        assert state.previous_justified_epoch > prev_state.previous_justified_epoch
+        assert state.previous_justified_root != prev_state.previous_justified_root
+    else:
+        assert state.previous_justified_epoch == prev_state.previous_justified_epoch
+        assert state.previous_justified_root == prev_state.previous_justified_root
+
+    if finalized_changed:
+        assert state.finalized_epoch > prev_state.finalized_epoch
+        assert state.finalized_root != prev_state.finalized_root
+    else:
+        assert state.finalized_epoch == prev_state.finalized_epoch
+        assert state.finalized_root == prev_state.finalized_root
+
+
 def test_slot_transition(state):
     test_state = deepcopy(state)
     cache_state(test_state)
@@ -116,6 +145,32 @@ def test_empty_epoch_transition_not_finalizing(state):
     return state, [block], test_state
 
 
+def test_full_attestations_finalizing(state):
+    test_state = deepcopy(state)
+
+    for slot in range(spec.MIN_ATTESTATION_INCLUSION_DELAY):
+        next_slot(test_state)
+
+    for epoch in range(5):
+        for slot in range(spec.SLOTS_PER_EPOCH):
+            attestation = get_valid_attestation(test_state, test_state.slot - spec.MIN_ATTESTATION_INCLUSION_DELAY)
+            fill_aggregate_attestation(test_state, attestation)
+            block = build_empty_block_for_next_slot(test_state)
+            block.body.attestations.append(attestation)
+            state_transition(test_state, block)
+
+        if epoch == 0:
+            check_finality(test_state, state, False, False, False)
+        elif epoch == 1:
+            check_finality(test_state, state, False, False, False)
+        elif epoch == 2:
+            check_finality(test_state, state, True, False, False)
+        elif epoch == 3:
+            check_finality(test_state, state, True, True, False)
+        elif epoch == 4:
+            check_finality(test_state, state, True, True, True)
+
+
 def test_proposer_slashing(state):
     test_state = deepcopy(state)
     proposer_slashing = get_valid_proposer_slashing(state)