Move more unit tests to test vectors

tests/core/pyspec/eth2spec/test/helpers/attestations.py

@@ -217,30 +217,13 @@ def next_slots_with_attestations(spec,
     post_state = state.copy()
     signed_blocks = []
     for _ in range(slot_count):
-        block = build_empty_block_for_next_slot(spec, post_state)
+        signed_block = state_transition_with_full_block(
-        if fill_cur_epoch and post_state.slot >= spec.MIN_ATTESTATION_INCLUSION_DELAY:
-            slot_to_attest = post_state.slot - spec.MIN_ATTESTATION_INCLUSION_DELAY + 1
-            if slot_to_attest >= spec.compute_start_slot_at_epoch(spec.get_current_epoch(post_state)):
-                attestations = _get_valid_attestation_at_slot(
-                    post_state,
             spec,
-                    slot_to_attest,
-                    participation_fn=participation_fn
-                )
-                for attestation in attestations:
-                    block.body.attestations.append(attestation)
-        if fill_prev_epoch:
-            slot_to_attest = post_state.slot - spec.SLOTS_PER_EPOCH + 1
-            attestations = _get_valid_attestation_at_slot(
             post_state,
-                spec,
+            fill_cur_epoch,
-                slot_to_attest,
+            fill_prev_epoch,
-                participation_fn=participation_fn
+            participation_fn,
         )
-            for attestation in attestations:
-                block.body.attestations.append(attestation)
-
-        signed_block = state_transition_and_sign_block(spec, post_state, block)
         signed_blocks.append(signed_block)
 
     return state, signed_blocks, post_state
@@ -249,7 +232,8 @@ def next_slots_with_attestations(spec,
 def next_epoch_with_attestations(spec,
                                  state,
                                  fill_cur_epoch,
-                                 fill_prev_epoch):
+                                 fill_prev_epoch,
+                                 participation_fn=None):
     assert state.slot % spec.SLOTS_PER_EPOCH == 0
 
     return next_slots_with_attestations(
@@ -258,15 +242,50 @@ def next_epoch_with_attestations(spec,
         spec.SLOTS_PER_EPOCH,
         fill_cur_epoch,
         fill_prev_epoch,
+        participation_fn,
     )
 
 
-def state_transition_with_signed_full_block(spec, state, fill_cur_epoch, fill_prev_epoch):
+def state_transition_with_full_block(spec, state, fill_cur_epoch, fill_prev_epoch, participation_fn=None):
+    """
+    Build and apply a block with attestions at the calculated `slot_to_attest` of current epoch and/or previous epoch.
+    """
+    block = build_empty_block_for_next_slot(spec, state)
+    if fill_cur_epoch and state.slot >= spec.MIN_ATTESTATION_INCLUSION_DELAY:
+        slot_to_attest = state.slot - spec.MIN_ATTESTATION_INCLUSION_DELAY + 1
+        if slot_to_attest >= spec.compute_start_slot_at_epoch(spec.get_current_epoch(state)):
+            attestations = _get_valid_attestation_at_slot(
+                state,
+                spec,
+                slot_to_attest,
+                participation_fn=participation_fn
+            )
+            for attestation in attestations:
+                block.body.attestations.append(attestation)
+    if fill_prev_epoch:
+        slot_to_attest = state.slot - spec.SLOTS_PER_EPOCH + 1
+        attestations = _get_valid_attestation_at_slot(
+            state,
+            spec,
+            slot_to_attest,
+            participation_fn=participation_fn
+        )
+        for attestation in attestations:
+            block.body.attestations.append(attestation)
+
+    signed_block = state_transition_and_sign_block(spec, state, block)
+    return signed_block
+
+
+def state_transition_with_full_attestations_block(spec, state, fill_cur_epoch, fill_prev_epoch):
+    """
+    Build and apply a block with attestions at all valid slots of current epoch and/or previous epoch.
+    """
     # Build a block with previous attestations
     block = build_empty_block_for_next_slot(spec, state)
     attestations = []
 
-    if fill_prev_epoch:
+    if fill_cur_epoch:
         # current epoch
         slots = state.slot % spec.SLOTS_PER_EPOCH
         for slot_offset in range(slots):

tests/core/pyspec/eth2spec/test/helpers/fork_choice.py

@@ -1,5 +1,8 @@
 from eth_utils import encode_hex
-from eth2spec.test.helpers.attestations import next_epoch_with_attestations
+from eth2spec.test.helpers.attestations import (
+    next_epoch_with_attestations,
+    next_slots_with_attestations,
+)
 
 
 def get_anchor_root(spec, state):
@@ -19,23 +22,20 @@ def add_block_to_store(spec, store, signed_block):
     spec.on_block(store, signed_block)
 
 
-def tick_and_add_block(spec, store, signed_block, test_steps=None, valid=True):
+def tick_and_add_block(spec, store, signed_block, test_steps, valid=True, allow_invalid_attestations=False):
-    if test_steps is None:
-        test_steps = []
-
     pre_state = store.block_states[signed_block.message.parent_root]
     block_time = pre_state.genesis_time + signed_block.message.slot * spec.config.SECONDS_PER_SLOT
 
     if store.time < block_time:
         on_tick_and_append_step(spec, store, block_time, test_steps)
 
-    yield from add_block(spec, store, signed_block, test_steps, valid=valid)
+    post_state = yield from add_block(
+        spec, store, signed_block, test_steps, valid=valid, allow_invalid_attestations=allow_invalid_attestations)
+
+    return post_state
 
 
-def tick_and_run_on_attestation(spec, store, attestation, test_steps=None):
+def tick_and_run_on_attestation(spec, store, attestation, test_steps):
-    if test_steps is None:
-        test_steps = []
-
     parent_block = store.blocks[attestation.data.beacon_block_root]
     pre_state = store.block_states[spec.hash_tree_root(parent_block)]
     block_time = pre_state.genesis_time + parent_block.slot * spec.config.SECONDS_PER_SLOT
@@ -50,6 +50,37 @@ def tick_and_run_on_attestation(spec, store, attestation, test_steps=None):
     test_steps.append({'attestation': get_attestation_file_name(attestation)})
 
 
+def add_attestation(spec, store, attestation, test_steps, valid=True):
+    yield get_attestation_file_name(attestation), attestation
+
+    if not valid:
+        try:
+            run_on_attestation(spec, store, attestation, valid=True)
+        except AssertionError:
+            test_steps.append({
+                'attestation': get_attestation_file_name(attestation),
+                'valid': False,
+            })
+            return
+        else:
+            assert False
+
+    run_on_attestation(spec, store, attestation, valid=True)
+    test_steps.append({'attestation': get_attestation_file_name(attestation)})
+
+
+def run_on_attestation(spec, store, attestation, valid=True):
+    if not valid:
+        try:
+            spec.on_attestation(store, attestation)
+        except AssertionError:
+            return
+        else:
+            assert False
+
+    spec.on_attestation(store, attestation)
+
+
 def get_genesis_forkchoice_store(spec, genesis_state):
     store, _ = get_genesis_forkchoice_store_and_block(spec, genesis_state)
     return store
@@ -87,10 +118,10 @@ def run_on_block(spec, store, signed_block, valid=True):
     assert store.blocks[signed_block.message.hash_tree_root()] == signed_block.message
 
 
-def add_block(spec, store, signed_block, test_steps=None, valid=True):
+def add_block(spec, store, signed_block, test_steps, valid=True, allow_invalid_attestations=False):
-    if test_steps is None:
+    """
-        test_steps = []
+    Run on_block and on_attestation
-
+    """
     yield get_block_file_name(signed_block), signed_block
 
     if not valid:
@@ -109,8 +140,14 @@ def add_block(spec, store, signed_block, test_steps=None, valid=True):
     test_steps.append({'block': get_block_file_name(signed_block)})
 
     # An on_block step implies receiving block's attestations
+    try:
         for attestation in signed_block.message.body.attestations:
-        spec.on_attestation(store, attestation)
+            run_on_attestation(spec, store, attestation, valid=True)
+    except AssertionError:
+        if allow_invalid_attestations:
+            pass
+        else:
+            raise
 
     block_root = signed_block.message.hash_tree_root()
     assert store.blocks[block_root] == signed_block.message
@@ -125,6 +162,8 @@ def add_block(spec, store, signed_block, test_steps=None, valid=True):
         }
     })
 
+    return store.block_states[signed_block.message.hash_tree_root()]
+
 
 def get_formatted_head_output(spec, store):
     head = spec.get_head(store)
@@ -135,11 +174,40 @@ def get_formatted_head_output(spec, store):
     }
 
 
-def apply_next_epoch_with_attestations(spec, state, store, test_steps=None):
+def apply_next_epoch_with_attestations(spec,
+                                       state,
+                                       store,
+                                       fill_cur_epoch,
+                                       fill_prev_epoch,
+                                       participation_fn=None,
+                                       test_steps=None):
     if test_steps is None:
         test_steps = []
 
-    _, new_signed_blocks, post_state = next_epoch_with_attestations(spec, state, True, False)
+    _, new_signed_blocks, post_state = next_epoch_with_attestations(
+        spec, state, fill_cur_epoch, fill_prev_epoch, participation_fn=participation_fn)
+    for signed_block in new_signed_blocks:
+        block = signed_block.message
+        yield from tick_and_add_block(spec, store, signed_block, test_steps)
+        block_root = block.hash_tree_root()
+        assert store.blocks[block_root] == block
+        last_signed_block = signed_block
+
+    assert store.block_states[block_root].hash_tree_root() == post_state.hash_tree_root()
+
+    return post_state, store, last_signed_block
+
+
+def apply_next_slots_with_attestations(spec,
+                                       state,
+                                       store,
+                                       slots,
+                                       fill_cur_epoch,
+                                       fill_prev_epoch,
+                                       test_steps,
+                                       participation_fn=None):
+    _, new_signed_blocks, post_state = next_slots_with_attestations(
+        spec, state, slots, fill_cur_epoch, fill_prev_epoch, participation_fn=participation_fn)
     for signed_block in new_signed_blocks:
         block = signed_block.message
         yield from tick_and_add_block(spec, store, signed_block, test_steps)

tests/core/pyspec/eth2spec/test/phase0/fork_choice/test_on_block.py

@@ -1,6 +1,13 @@
-from eth2spec.utils.ssz.ssz_impl import hash_tree_root
+import random
 
+from eth2spec.utils.ssz.ssz_impl import hash_tree_root
 from eth2spec.test.context import MINIMAL, spec_state_test, with_all_phases, with_presets
+from eth2spec.test.helpers.attestations import (
+    next_epoch_with_attestations,
+    next_slots_with_attestations,
+    state_transition_with_full_block,
+    state_transition_with_full_attestations_block,
+)
 from eth2spec.test.helpers.block import (
     build_empty_block_for_next_slot,
     build_empty_block,
@@ -13,14 +20,27 @@ from eth2spec.test.helpers.fork_choice import (
     add_block,
     tick_and_add_block,
     apply_next_epoch_with_attestations,
+    apply_next_slots_with_attestations,
 )
 from eth2spec.test.helpers.state import (
     next_epoch,
+    next_slots,
     state_transition_and_sign_block,
     transition_to,
 )
 
 
+rng = random.Random(2020)
+
+
+def _drop_random_one_third(_slot, _index, indices):
+    committee_len = len(indices)
+    assert committee_len >= 3
+    filter_len = committee_len // 3
+    participant_count = committee_len - filter_len
+    return rng.sample(indices, participant_count)
+
+
 @with_all_phases
 @spec_state_test
 def test_basic(spec, state):
@@ -68,7 +88,8 @@ def test_on_block_checkpoints(spec, state):
     next_epoch(spec, state)
     on_tick_and_append_step(spec, store, store.time + state.slot * spec.config.SECONDS_PER_SLOT, test_steps)
 
-    state, store, last_signed_block = yield from apply_next_epoch_with_attestations(spec, state, store, test_steps)
+    state, store, last_signed_block = yield from apply_next_epoch_with_attestations(
+        spec, state, store, True, False, test_steps=test_steps)
     last_block_root = hash_tree_root(last_signed_block.message)
     assert spec.get_head(store) == last_block_root
 
@@ -152,7 +173,8 @@ def test_on_block_before_finalized(spec, state):
 
     # Create a finalized chain
     for _ in range(4):
-        state, store, _ = yield from apply_next_epoch_with_attestations(spec, state, store, test_steps)
+        state, store, _ = yield from apply_next_epoch_with_attestations(
+            spec, state, store, True, False, test_steps=test_steps)
     assert store.finalized_checkpoint.epoch == 2
 
     # Fail receiving block of `GENESIS_SLOT + 1` slot
@@ -180,7 +202,8 @@ def test_on_block_finalized_skip_slots(spec, state):
 
     # Create a finalized chain
     for _ in range(4):
-        state, store, _ = yield from apply_next_epoch_with_attestations(spec, state, store, test_steps)
+        state, store, _ = yield from apply_next_epoch_with_attestations(
+            spec, state, store, True, False, test_steps=test_steps)
     assert store.finalized_checkpoint.epoch == 2
 
     # Another chain
@@ -219,7 +242,8 @@ def test_on_block_finalized_skip_slots_not_in_skip_chain(spec, state):
 
     # Finalized
     for _ in range(3):
-        state, store, _ = yield from apply_next_epoch_with_attestations(spec, state, store, test_steps)
+        state, store, _ = yield from apply_next_epoch_with_attestations(
+            spec, state, store, True, False, test_steps=test_steps)
     assert store.finalized_checkpoint.epoch == pre_finalized_checkpoint_epoch + 1
 
     # Now build a block at later slot than finalized epoch
@@ -233,3 +257,435 @@ def test_on_block_finalized_skip_slots_not_in_skip_chain(spec, state):
     yield from tick_and_add_block(spec, store, signed_block, test_steps, valid=False)
 
     yield 'steps', test_steps
+
+
+@with_all_phases
+@spec_state_test
+@with_presets([MINIMAL], reason="mainnet config requires too many pre-generated public/private keys")
+def test_on_block_update_justified_checkpoint_within_safe_slots(spec, state):
+    """
+    Test `should_update_justified_checkpoint`:
+    compute_slots_since_epoch_start(get_current_slot(store)) < SAFE_SLOTS_TO_UPDATE_JUSTIFIED
+    """
+    test_steps = []
+    # Initialization
+    store, anchor_block = get_genesis_forkchoice_store_and_block(spec, state)
+    yield 'anchor_state', state
+    yield 'anchor_block', anchor_block
+    current_time = state.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, current_time, test_steps)
+    assert store.time == current_time
+
+    # Skip epoch 0 & 1
+    for _ in range(2):
+        next_epoch(spec, state)
+    # Fill epoch 2
+    state, store, _ = yield from apply_next_epoch_with_attestations(
+        spec, state, store, True, False, test_steps=test_steps)
+    assert state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 0
+    assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 2
+    # Skip epoch 3 & 4
+    for _ in range(2):
+        next_epoch(spec, state)
+    # Epoch 5: Attest current epoch
+    state, store, _ = yield from apply_next_epoch_with_attestations(
+        spec, state, store, True, False, participation_fn=_drop_random_one_third, test_steps=test_steps)
+    assert state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 0
+    assert state.current_justified_checkpoint.epoch == 2
+    assert store.justified_checkpoint.epoch == 2
+    assert state.current_justified_checkpoint == store.justified_checkpoint
+
+    # Skip epoch 6
+    next_epoch(spec, state)
+
+    pre_state = state.copy()
+
+    # Build a block to justify epoch 5
+    signed_block = state_transition_with_full_block(spec, state, True, True)
+    assert state.finalized_checkpoint.epoch == 0
+    assert state.current_justified_checkpoint.epoch == 5
+    assert state.current_justified_checkpoint.epoch > store.justified_checkpoint.epoch
+    assert spec.get_current_slot(store) % spec.SLOTS_PER_EPOCH < spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED
+    # Run on_block
+    yield from tick_and_add_block(spec, store, signed_block, test_steps)
+    # Ensure justified_checkpoint has been changed but finality is unchanged
+    assert store.justified_checkpoint.epoch == 5
+    assert store.justified_checkpoint == state.current_justified_checkpoint
+    assert store.finalized_checkpoint.epoch == pre_state.finalized_checkpoint.epoch == 0
+
+    yield 'steps', test_steps
+
+
+@with_all_phases
+@with_presets([MINIMAL], reason="It assumes that `MAX_ATTESTATIONS` >= 2/3 attestations of an epoch")
+@spec_state_test
+def test_on_block_outside_safe_slots_but_finality(spec, state):
+    """
+    Test `should_update_justified_checkpoint` case
+    - compute_slots_since_epoch_start(get_current_slot(store)) > SAFE_SLOTS_TO_UPDATE_JUSTIFIED
+    - new_justified_checkpoint and store.justified_checkpoint.root are NOT conflicting
+
+    Thus should_update_justified_checkpoint returns True.
+
+    Part of this script is similar to `test_new_justified_is_later_than_store_justified`.
+    """
+    test_steps = []
+    # Initialization
+    store, anchor_block = get_genesis_forkchoice_store_and_block(spec, state)
+    yield 'anchor_state', state
+    yield 'anchor_block', anchor_block
+    current_time = state.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, current_time, test_steps)
+    assert store.time == current_time
+
+    # Skip epoch 0
+    next_epoch(spec, state)
+    # Fill epoch 1 to 3, attest current epoch
+    for _ in range(3):
+        state, store, _ = yield from apply_next_epoch_with_attestations(
+            spec, state, store, True, False, test_steps=test_steps)
+    assert state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 2
+    assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
+
+    # Skip epoch 4-6
+    for _ in range(3):
+        next_epoch(spec, state)
+
+    # epoch 7
+    state, store, _ = yield from apply_next_epoch_with_attestations(
+        spec, state, store, True, True, test_steps=test_steps)
+    assert state.finalized_checkpoint.epoch == 2
+    assert state.current_justified_checkpoint.epoch == 7
+
+    # epoch 8, attest the first 5 blocks
+    state, store, _ = yield from apply_next_slots_with_attestations(
+        spec, state, store, 5, True, True, test_steps)
+    assert state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 2
+    assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 7
+
+    # Propose a block at epoch 9, 5th slot
+    next_epoch(spec, state)
+    next_slots(spec, state, 4)
+    signed_block = state_transition_with_full_attestations_block(spec, state, True, True)
+    yield from tick_and_add_block(spec, store, signed_block, test_steps)
+    assert state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 2
+    assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 7
+
+    # Propose an empty block at epoch 10, SAFE_SLOTS_TO_UPDATE_JUSTIFIED + 2 slot
+    # This block would trigger justification and finality updates on store
+    next_epoch(spec, state)
+    next_slots(spec, state, 4)
+    block = build_empty_block_for_next_slot(spec, state)
+    signed_block = state_transition_and_sign_block(spec, state, block)
+    assert state.finalized_checkpoint.epoch == 7
+    assert state.current_justified_checkpoint.epoch == 8
+    # Step time past safe slots and run on_block
+    if store.time < spec.compute_time_at_slot(state, signed_block.message.slot):
+        time = store.genesis_time + signed_block.message.slot * spec.config.SECONDS_PER_SLOT
+        on_tick_and_append_step(spec, store, time, test_steps)
+    assert spec.get_current_slot(store) % spec.SLOTS_PER_EPOCH >= spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED
+    yield from add_block(spec, store, signed_block, test_steps)
+
+    # Ensure justified_checkpoint finality has been changed
+    assert store.finalized_checkpoint.epoch == 7
+    assert store.finalized_checkpoint == state.finalized_checkpoint
+    assert store.justified_checkpoint.epoch == 8
+    assert store.justified_checkpoint == state.current_justified_checkpoint
+
+    yield 'steps', test_steps
+
+
+@with_all_phases
+@with_presets([MINIMAL], reason="It assumes that `MAX_ATTESTATIONS` >= 2/3 attestations of an epoch")
+@spec_state_test
+def test_new_justified_is_later_than_store_justified(spec, state):
+    """
+    J: Justified
+    F: Finalized
+    fork_1_state (forked from genesis):
+        epoch
+        [0] <- [1] <- [2] <- [3] <- [4]
+         F                    J
+
+    fork_2_state (forked from fork_1_state's epoch 2):
+        epoch
+                       └──── [3] <- [4] <- [5] <- [6]
+         F                           J
+
+    fork_3_state (forked from genesis):
+        [0] <- [1] <- [2] <- [3] <- [4] <- [5]
+                              F      J
+    """
+    # The 1st fork, from genesis
+    fork_1_state = state.copy()
+    # The 3rd fork, from genesis
+    fork_3_state = state.copy()
+
+    test_steps = []
+    # Initialization
+    store, anchor_block = get_genesis_forkchoice_store_and_block(spec, state)
+    yield 'anchor_state', state
+    yield 'anchor_block', anchor_block
+    current_time = state.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, current_time, test_steps)
+    assert store.time == current_time
+
+    # ----- Process fork_1_state
+    # Skip epoch 0
+    next_epoch(spec, fork_1_state)
+    # Fill epoch 1 with previous epoch attestations
+    fork_1_state, store, _ = yield from apply_next_epoch_with_attestations(
+        spec, fork_1_state, store, False, True, test_steps=test_steps)
+
+    # Fork `fork_2_state` at the start of epoch 2
+    fork_2_state = fork_1_state.copy()
+    assert spec.get_current_epoch(fork_2_state) == 2
+
+    # Skip epoch 2
+    next_epoch(spec, fork_1_state)
+    # # Fill epoch 3 & 4 with previous epoch attestations
+    for _ in range(2):
+        fork_1_state, store, _ = yield from apply_next_epoch_with_attestations(
+            spec, fork_1_state, store, False, True, test_steps=test_steps)
+
+    assert fork_1_state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 0
+    assert fork_1_state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
+    assert store.justified_checkpoint == fork_1_state.current_justified_checkpoint
+
+    # ------ fork_2_state: Create a chain to set store.best_justified_checkpoint
+    # NOTE: The goal is to make `store.best_justified_checkpoint.epoch > store.justified_checkpoint.epoch`
+    all_blocks = []
+
+    # Proposed an empty block at epoch 2, 1st slot
+    block = build_empty_block_for_next_slot(spec, fork_2_state)
+    signed_block = state_transition_and_sign_block(spec, fork_2_state, block)
+    yield from tick_and_add_block(spec, store, signed_block, test_steps)
+    assert fork_2_state.current_justified_checkpoint.epoch == 0
+
+    # Skip to epoch 4
+    for _ in range(2):
+        next_epoch(spec, fork_2_state)
+        assert fork_2_state.current_justified_checkpoint.epoch == 0
+
+    # Propose a block at epoch 4, 5th slot
+    # Propose a block at epoch 5, 5th slot
+    for _ in range(2):
+        next_epoch(spec, fork_2_state)
+        next_slots(spec, fork_2_state, 4)
+        signed_block = state_transition_with_full_attestations_block(spec, fork_2_state, True, True)
+        yield from tick_and_add_block(spec, store, signed_block, test_steps)
+        assert fork_2_state.current_justified_checkpoint.epoch == 0
+
+    # Propose a block at epoch 6, SAFE_SLOTS_TO_UPDATE_JUSTIFIED + 2 slot
+    next_epoch(spec, fork_2_state)
+    next_slots(spec, fork_2_state, spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED + 2)
+    signed_block = state_transition_with_full_attestations_block(spec, fork_2_state, True, True)
+    assert fork_2_state.finalized_checkpoint.epoch == 0
+    assert fork_2_state.current_justified_checkpoint.epoch == 5
+    # Check SAFE_SLOTS_TO_UPDATE_JUSTIFIED
+    spec.on_tick(store, store.genesis_time + fork_2_state.slot * spec.config.SECONDS_PER_SLOT)
+    assert spec.compute_slots_since_epoch_start(spec.get_current_slot(store)) >= spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED
+    # Run on_block
+    yield from add_block(spec, store, signed_block, test_steps)
+    assert store.finalized_checkpoint.epoch == 0
+    assert store.justified_checkpoint.epoch == 3
+    assert store.best_justified_checkpoint.epoch == 5
+
+    # ------ fork_3_state: Create another chain to test the
+    # "Update justified if new justified is later than store justified" case
+    all_blocks = []
+    for _ in range(3):
+        next_epoch(spec, fork_3_state)
+
+    # epoch 3
+    _, signed_blocks, fork_3_state = next_epoch_with_attestations(spec, fork_3_state, True, True)
+    all_blocks += signed_blocks
+    assert fork_3_state.finalized_checkpoint.epoch == 0
+
+    # epoch 4, attest the first 5 blocks
+    _, blocks, fork_3_state = next_slots_with_attestations(spec, fork_3_state, 5, True, True)
+    all_blocks += blocks.copy()
+    assert fork_3_state.finalized_checkpoint.epoch == 0
+
+    # Propose a block at epoch 5, 5th slot
+    next_epoch(spec, fork_3_state)
+    next_slots(spec, fork_3_state, 4)
+    signed_block = state_transition_with_full_block(spec, fork_3_state, True, True)
+    all_blocks.append(signed_block.copy())
+    assert fork_3_state.finalized_checkpoint.epoch == 0
+
+    # Propose a block at epoch 6, 5th slot
+    next_epoch(spec, fork_3_state)
+    next_slots(spec, fork_3_state, 4)
+    signed_block = state_transition_with_full_block(spec, fork_3_state, True, True)
+    all_blocks.append(signed_block.copy())
+    assert fork_3_state.finalized_checkpoint.epoch == 3
+    assert fork_3_state.current_justified_checkpoint.epoch == 4
+
+    # FIXME: pending on the `on_block`, `on_attestation` fix
+    # # Apply blocks of `fork_3_state` to `store`
+    # for block in all_blocks:
+    #     if store.time < spec.compute_time_at_slot(fork_2_state, block.message.slot):
+    #         spec.on_tick(store, store.genesis_time + block.message.slot * spec.config.SECONDS_PER_SLOT)
+    #     # valid_attestations=False because the attestations are outdated (older than previous epoch)
+    #     yield from add_block(spec, store, block, test_steps, allow_invalid_attestations=False)
+
+    # assert store.finalized_checkpoint == fork_3_state.finalized_checkpoint
+    # assert (store.justified_checkpoint
+    #         == fork_3_state.current_justified_checkpoint
+    #         != store.best_justified_checkpoint)
+    # assert (store.best_justified_checkpoint
+    #         == fork_2_state.current_justified_checkpoint)
+
+    yield 'steps', test_steps
+
+
+@with_all_phases
+@spec_state_test
+def test_new_finalized_slot_is_not_justified_checkpoint_ancestor(spec, state):
+    """
+    J: Justified
+    F: Finalized
+    state (forked from genesis):
+        epoch
+        [0] <- [1] <- [2] <- [3] <- [4] <- [5]
+         F                    J
+
+    another_state (forked from epoch 0):
+         └──── [1] <- [2] <- [3] <- [4] <- [5]
+                       F      J
+    """
+    test_steps = []
+    # Initialization
+    store, anchor_block = get_genesis_forkchoice_store_and_block(spec, state)
+    yield 'anchor_state', state
+    yield 'anchor_block', anchor_block
+    current_time = state.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, current_time, test_steps)
+    assert store.time == current_time
+
+    # ----- Process state
+    # Goal: make `store.finalized_checkpoint.epoch == 0` and `store.justified_checkpoint.epoch == 3`
+    # Skip epoch 0
+    next_epoch(spec, state)
+
+    # Forking another_state
+    another_state = state.copy()
+
+    # Fill epoch 1 with previous epoch attestations
+    state, store, _ = yield from apply_next_epoch_with_attestations(
+        spec, state, store, False, True, test_steps=test_steps)
+    # Skip epoch 2
+    next_epoch(spec, state)
+    # Fill epoch 3 & 4 with previous epoch attestations
+    for _ in range(2):
+        state, store, _ = yield from apply_next_epoch_with_attestations(
+            spec, state, store, False, True, test_steps=test_steps)
+
+    assert state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 0
+    assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
+    assert store.justified_checkpoint == state.current_justified_checkpoint
+
+    # Create another chain
+    # Goal: make `another_state.finalized_checkpoint.epoch == 2` and `another_state.justified_checkpoint.epoch == 3`
+    all_blocks = []
+    # Fill epoch 1 & 2 with previous + current epoch attestations
+    for _ in range(3):
+        _, signed_blocks, another_state = next_epoch_with_attestations(spec, another_state, True, True)
+        all_blocks += signed_blocks
+
+    assert another_state.finalized_checkpoint.epoch == 2
+    assert another_state.current_justified_checkpoint.epoch == 3
+    assert state.finalized_checkpoint.hash_tree_root() != another_state.finalized_checkpoint.hash_tree_root()
+    assert (
+        state.current_justified_checkpoint.hash_tree_root()
+        != another_state.current_justified_checkpoint.hash_tree_root()
+    )
+    # pre_store_justified_checkpoint_root = store.justified_checkpoint.root
+
+    # FIXME: pending on the `on_block`, `on_attestation` fix
+    # # Apply blocks of `another_state` to `store`
+    # for block in all_blocks:
+    #     # NOTE: Do not call `on_tick` here
+    #     yield from add_block(spec, store, block, test_steps, allow_invalid_attestations=True)
+
+    # finalized_slot = spec.compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
+    # ancestor_at_finalized_slot = spec.get_ancestor(store, pre_store_justified_checkpoint_root, finalized_slot)
+    # assert ancestor_at_finalized_slot != store.finalized_checkpoint.root
+
+    # assert store.finalized_checkpoint == another_state.finalized_checkpoint
+    # assert store.justified_checkpoint == another_state.current_justified_checkpoint
+
+    yield 'steps', test_steps
+
+
+@with_all_phases
+@spec_state_test
+def test_new_finalized_slot_is_justified_checkpoint_ancestor(spec, state):
+    """
+    J: Justified
+    F: Finalized
+    state:
+        epoch
+        [0] <- [1] <- [2] <- [3] <- [4] <- [5]
+                       F             J
+
+    another_state (forked from state at epoch 3):
+                              └──── [4] <- [5]
+                              F      J
+    """
+    test_steps = []
+    # Initialization
+    store, anchor_block = get_genesis_forkchoice_store_and_block(spec, state)
+    yield 'anchor_state', state
+    yield 'anchor_block', anchor_block
+    current_time = state.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, current_time, test_steps)
+    assert store.time == current_time
+
+    # Process state
+    next_epoch(spec, state)
+    spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
+
+    state, store, _ = yield from apply_next_epoch_with_attestations(
+        spec, state, store, False, True, test_steps=test_steps)
+
+    state, store, _ = yield from apply_next_epoch_with_attestations(
+        spec, state, store, True, False, test_steps=test_steps)
+    next_epoch(spec, state)
+
+    for _ in range(2):
+        state, store, _ = yield from apply_next_epoch_with_attestations(
+            spec, state, store, False, True, test_steps=test_steps)
+
+    assert state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 2
+    assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 4
+    assert store.justified_checkpoint == state.current_justified_checkpoint
+
+    # Create another chain
+    # Forking from epoch 3
+    all_blocks = []
+    slot = spec.compute_start_slot_at_epoch(3)
+    block_root = spec.get_block_root_at_slot(state, slot)
+    another_state = store.block_states[block_root].copy()
+    for _ in range(2):
+        _, signed_blocks, another_state = next_epoch_with_attestations(spec, another_state, True, True)
+        all_blocks += signed_blocks
+
+    assert another_state.finalized_checkpoint.epoch == 3
+    assert another_state.current_justified_checkpoint.epoch == 4
+
+    pre_store_justified_checkpoint_root = store.justified_checkpoint.root
+    for block in all_blocks:
+        # FIXME: Once `on_block` and `on_attestation` logic is fixed,
+        # fix test case and remove allow_invalid_attestations flag
+        yield from tick_and_add_block(spec, store, block, test_steps, allow_invalid_attestations=True)
+
+    finalized_slot = spec.compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
+    ancestor_at_finalized_slot = spec.get_ancestor(store, pre_store_justified_checkpoint_root, finalized_slot)
+    assert ancestor_at_finalized_slot == store.finalized_checkpoint.root
+
+    assert store.finalized_checkpoint == another_state.finalized_checkpoint
+    assert store.justified_checkpoint != another_state.current_justified_checkpoint
+
+    yield 'steps', test_steps

tests/core/pyspec/eth2spec/test/phase0/unittests/fork_choice/test_on_block.py

@@ -1,11 +1,9 @@
 from copy import deepcopy
-from eth2spec.utils.ssz.ssz_impl import hash_tree_root
 
-from eth2spec.test.context import MINIMAL, with_all_phases, spec_state_test, with_presets
+from eth2spec.utils.ssz.ssz_impl import hash_tree_root
-from eth2spec.test.helpers.attestations import (
+from eth2spec.test.context import (
-    next_epoch_with_attestations,
+    spec_state_test,
-    next_slots_with_attestations,
+    with_all_phases,
-    state_transition_with_signed_full_block,
 )
 from eth2spec.test.helpers.block import (
     build_empty_block_for_next_slot,
@@ -15,58 +13,25 @@ from eth2spec.test.helpers.fork_choice import (
     run_on_block,
     apply_next_epoch_with_attestations,
 )
-from eth2spec.test.helpers.state import next_epoch, state_transition_and_sign_block, next_slots
+from eth2spec.test.helpers.state import (
-
+    next_epoch,
-
+    state_transition_and_sign_block,
-@with_all_phases
-@spec_state_test
-def test_on_block_update_justified_checkpoint_within_safe_slots(spec, state):
-    # Initialization
-    store = get_genesis_forkchoice_store(spec, state)
-
-    next_epoch(spec, state)
-    spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-    state, store, last_signed_block = yield from apply_next_epoch_with_attestations(spec, state, store)
-    next_epoch(spec, state)
-    spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-    last_block_root = last_signed_block.message.hash_tree_root()
-
-    # NOTE: Mock the justified checkpoint
-    just_state = store.block_states[last_block_root]
-    new_justified = spec.Checkpoint(
-        epoch=just_state.current_justified_checkpoint.epoch + 1,
-        root=b'\x77' * 32,
 )
-    just_state.current_justified_checkpoint = new_justified  # Mutate `store`
-
-    assert store.block_states[last_block_root].hash_tree_root() == just_state.hash_tree_root()
-
-    block = build_empty_block_for_next_slot(spec, just_state)
-
-    # NOTE: Mock store so that the modified state could be accessed
-    parent_block = last_signed_block.message.copy()
-    parent_block.state_root = just_state.hash_tree_root()
-    store.blocks[block.parent_root] = parent_block
-    store.block_states[block.parent_root] = just_state.copy()
-    assert block.parent_root in store.blocks.keys()
-    assert block.parent_root in store.block_states.keys()
-
-    signed_block = state_transition_and_sign_block(spec, just_state.copy(), block)
-    assert spec.get_current_slot(store) % spec.SLOTS_PER_EPOCH < spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED
-    run_on_block(spec, store, signed_block)
-
-    assert store.justified_checkpoint == new_justified
 
 
 @with_all_phases
 @spec_state_test
 def test_on_block_outside_safe_slots_and_multiple_better_justified(spec, state):
+    """
+    NOTE: test_new_justified_is_later_than_store_justified also tests best_justified_checkpoint
+    """
     # Initialization
     store = get_genesis_forkchoice_store(spec, state)
 
     next_epoch(spec, state)
     spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-    state, store, last_signed_block = yield from apply_next_epoch_with_attestations(spec, state, store)
+    state, store, last_signed_block = yield from apply_next_epoch_with_attestations(
+        spec, state, store, True, False)
     last_block_root = hash_tree_root(last_signed_block.message)
 
     # NOTE: Mock fictitious justified checkpoint in store
@@ -86,6 +51,7 @@ def test_on_block_outside_safe_slots_and_multiple_better_justified(spec, state):
     spec.on_tick(store, store.time + spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED * spec.config.SECONDS_PER_SLOT)
     assert spec.get_current_slot(store) % spec.SLOTS_PER_EPOCH >= spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED
 
+    previously_finalized = store.finalized_checkpoint
     previously_justified = store.justified_checkpoint
 
     # Add a series of new blocks with "better" justifications
@@ -115,355 +81,7 @@ def test_on_block_outside_safe_slots_and_multiple_better_justified(spec, state):
 
         run_on_block(spec, store, signed_block)
 
+    assert store.finalized_checkpoint == previously_finalized
     assert store.justified_checkpoint == previously_justified
     # ensure the best from the series was stored
     assert store.best_justified_checkpoint == best_justified_checkpoint
-
-
-@with_all_phases
-@spec_state_test
-def test_on_block_outside_safe_slots_but_finality(spec, state):
-    # Initialization
-    store = get_genesis_forkchoice_store(spec, state)
-
-    next_epoch(spec, state)
-    spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-    state, store, last_signed_block = yield from apply_next_epoch_with_attestations(spec, state, store)
-    last_block_root = hash_tree_root(last_signed_block.message)
-
-    # NOTE: Mock fictitious justified checkpoint in store
-    store.justified_checkpoint = spec.Checkpoint(
-        epoch=spec.compute_epoch_at_slot(last_signed_block.message.slot),
-        root=spec.Root("0x4a55535449464945440000000000000000000000000000000000000000000000")
-    )
-
-    next_epoch(spec, state)
-    spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-
-    # NOTE: Mock a new higher justified checkpoint not in branch of store's justified checkpoint
-    just_block = build_empty_block_for_next_slot(spec, state)
-    store.blocks[just_block.hash_tree_root()] = just_block
-
-    # Step time past safe slots
-    spec.on_tick(store, store.time + spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED * spec.config.SECONDS_PER_SLOT)
-    assert spec.get_current_slot(store) % spec.SLOTS_PER_EPOCH >= spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED
-
-    # NOTE: Mock justified and finalized update in state
-    just_fin_state = store.block_states[last_block_root]
-    new_justified = spec.Checkpoint(
-        epoch=spec.compute_epoch_at_slot(just_block.slot) + 1,
-        root=just_block.hash_tree_root(),
-    )
-    assert new_justified.epoch > store.justified_checkpoint.epoch
-    new_finalized = spec.Checkpoint(
-        epoch=spec.compute_epoch_at_slot(just_block.slot),
-        root=just_block.parent_root,
-    )
-    assert new_finalized.epoch > store.finalized_checkpoint.epoch
-    just_fin_state.current_justified_checkpoint = new_justified
-    just_fin_state.finalized_checkpoint = new_finalized
-
-    # Build and add block that includes the new justified/finalized info
-    block = build_empty_block_for_next_slot(spec, just_fin_state)
-    signed_block = state_transition_and_sign_block(spec, deepcopy(just_fin_state), block)
-
-    # NOTE: Mock store so that the modified state could be accessed
-    parent_block = last_signed_block.message.copy()
-    parent_block.state_root = just_fin_state.hash_tree_root()
-    store.blocks[block.parent_root] = parent_block
-    store.block_states[block.parent_root] = just_fin_state.copy()
-    assert block.parent_root in store.blocks.keys()
-    assert block.parent_root in store.block_states.keys()
-
-    run_on_block(spec, store, signed_block)
-
-    assert store.finalized_checkpoint == new_finalized
-    assert store.justified_checkpoint == new_justified
-
-
-@with_all_phases
-@with_presets([MINIMAL], reason="It assumes that `MAX_ATTESTATIONS` >= 2/3 attestations of an epoch")
-@spec_state_test
-def test_new_justified_is_later_than_store_justified(spec, state):
-    """
-    J: Justified
-    F: Finalized
-    fork_1_state (forked from genesis):
-        epoch
-        [0] <- [1] <- [2] <- [3] <- [4]
-         F                    J
-
-    fork_2_state (forked from fork_1_state's epoch 2):
-        epoch
-                       └──── [3] <- [4] <- [5] <- [6]
-         F                           J
-
-    fork_3_state (forked from genesis):
-        [0] <- [1] <- [2] <- [3] <- [4] <- [5]
-                              F      J
-    """
-    # The 1st fork, from genesis
-    fork_1_state = state.copy()
-    # The 3rd fork, from genesis
-    fork_3_state = state.copy()
-
-    # Initialization
-    store = get_genesis_forkchoice_store(spec, fork_1_state)
-
-    # ----- Process fork_1_state
-    # Skip epoch 0
-    next_epoch(spec, fork_1_state)
-    # Fill epoch 1 with previous epoch attestations
-    _, signed_blocks, fork_1_state = next_epoch_with_attestations(spec, fork_1_state, False, True)
-    for block in signed_blocks:
-        spec.on_tick(store, store.genesis_time + fork_1_state.slot * spec.config.SECONDS_PER_SLOT)
-        run_on_block(spec, store, block)
-
-    # Fork `fork_2_state` at the start of epoch 2
-    fork_2_state = fork_1_state.copy()
-    assert spec.get_current_epoch(fork_2_state) == 2
-
-    # Skip epoch 2
-    next_epoch(spec, fork_1_state)
-    # # Fill epoch 3 & 4 with previous epoch attestations
-    for _ in range(2):
-        _, signed_blocks, fork_1_state = next_epoch_with_attestations(spec, fork_1_state, False, True)
-        for block in signed_blocks:
-            spec.on_tick(store, store.genesis_time + fork_1_state.slot * spec.config.SECONDS_PER_SLOT)
-            run_on_block(spec, store, block)
-
-    assert fork_1_state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 0
-    assert fork_1_state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
-    assert store.justified_checkpoint.hash_tree_root() == fork_1_state.current_justified_checkpoint.hash_tree_root()
-
-    # ------ fork_2_state: Create a chain to set store.best_justified_checkpoint
-    # NOTE: The goal is to make `store.best_justified_checkpoint.epoch > store.justified_checkpoint.epoch`
-    all_blocks = []
-
-    # Proposed an empty block at epoch 2, 1st slot
-    block = build_empty_block_for_next_slot(spec, fork_2_state)
-    signed_block = state_transition_and_sign_block(spec, fork_2_state, block)
-    all_blocks.append(signed_block.copy())
-    assert fork_2_state.current_justified_checkpoint.epoch == 0
-
-    # Skip to epoch 4
-    for _ in range(2):
-        next_epoch(spec, fork_2_state)
-        assert fork_2_state.current_justified_checkpoint.epoch == 0
-
-    # Propose a block at epoch 4, 5th slot
-    # Propose a block at epoch 5, 5th slot
-    for _ in range(2):
-        next_epoch(spec, fork_2_state)
-        next_slots(spec, fork_2_state, 4)
-        signed_block = state_transition_with_signed_full_block(spec, fork_2_state, True, True)
-        all_blocks.append(signed_block.copy())
-        assert fork_2_state.current_justified_checkpoint.epoch == 0
-
-    # Propose a block at epoch 6, SAFE_SLOTS_TO_UPDATE_JUSTIFIED + 2 slot
-    next_epoch(spec, fork_2_state)
-    next_slots(spec, fork_2_state, spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED + 2)
-    signed_block = state_transition_with_signed_full_block(spec, fork_2_state, True, True)
-    all_blocks.append(signed_block.copy())
-    assert fork_2_state.finalized_checkpoint.epoch == 0
-    assert fork_2_state.current_justified_checkpoint.epoch == 5
-
-    # Check SAFE_SLOTS_TO_UPDATE_JUSTIFIED
-    spec.on_tick(store, store.genesis_time + fork_2_state.slot * spec.config.SECONDS_PER_SLOT)
-    assert spec.compute_slots_since_epoch_start(spec.get_current_slot(store)) >= spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED
-
-    # Apply blocks of `fork_3_state` to `store`
-    for block in all_blocks:
-        if store.time < spec.compute_time_at_slot(fork_2_state, block.message.slot):
-            spec.on_tick(store, store.genesis_time + block.message.slot * spec.config.SECONDS_PER_SLOT)
-        run_on_block(spec, store, block)
-
-    assert store.finalized_checkpoint.epoch == 0
-    assert store.justified_checkpoint.epoch == 3
-    assert store.best_justified_checkpoint.epoch == 5
-
-    # ------ fork_3_state: Create another chain to test the
-    # "Update justified if new justified is later than store justified" case
-    all_blocks = []
-    for _ in range(3):
-        next_epoch(spec, fork_3_state)
-
-    # epoch 3
-    _, signed_blocks, fork_3_state = next_epoch_with_attestations(spec, fork_3_state, True, True)
-    all_blocks += signed_blocks
-    assert fork_3_state.finalized_checkpoint.epoch == 0
-
-    # epoch 4, attest the first 5 blocks
-    _, blocks, fork_3_state = next_slots_with_attestations(spec, fork_3_state, 5, True, True)
-    all_blocks += blocks.copy()
-    assert fork_3_state.finalized_checkpoint.epoch == 0
-
-    # Propose a block at epoch 5, 5th slot
-    next_epoch(spec, fork_3_state)
-    next_slots(spec, fork_3_state, 4)
-    signed_block = state_transition_with_signed_full_block(spec, fork_3_state, True, True)
-    all_blocks.append(signed_block.copy())
-    assert fork_3_state.finalized_checkpoint.epoch == 0
-
-    # Propose a block at epoch 6, 5th slot
-    next_epoch(spec, fork_3_state)
-    next_slots(spec, fork_3_state, 4)
-    signed_block = state_transition_with_signed_full_block(spec, fork_3_state, True, True)
-    all_blocks.append(signed_block.copy())
-    assert fork_3_state.finalized_checkpoint.epoch == 3
-    assert fork_3_state.current_justified_checkpoint.epoch == 4
-
-    # Apply blocks of `fork_3_state` to `store`
-    for block in all_blocks:
-        if store.time < spec.compute_time_at_slot(fork_2_state, block.message.slot):
-            spec.on_tick(store, store.genesis_time + block.message.slot * spec.config.SECONDS_PER_SLOT)
-        run_on_block(spec, store, block)
-
-    assert store.finalized_checkpoint.hash_tree_root() == fork_3_state.finalized_checkpoint.hash_tree_root()
-    assert (store.justified_checkpoint.hash_tree_root()
-            == fork_3_state.current_justified_checkpoint.hash_tree_root()
-            != store.best_justified_checkpoint.hash_tree_root())
-    assert (store.best_justified_checkpoint.hash_tree_root()
-            == fork_2_state.current_justified_checkpoint.hash_tree_root())
-
-
-@with_all_phases
-@spec_state_test
-def test_new_finalized_slot_is_not_justified_checkpoint_ancestor(spec, state):
-    """
-    J: Justified
-    F: Finalized
-    state (forked from genesis):
-        epoch
-        [0] <- [1] <- [2] <- [3] <- [4] <- [5]
-         F                    J
-
-    another_state (forked from epoch 0):
-         └──── [1] <- [2] <- [3] <- [4] <- [5]
-                       F      J
-    """
-    # Initialization
-    store = get_genesis_forkchoice_store(spec, state)
-
-    # ----- Process state
-    # Goal: make `store.finalized_checkpoint.epoch == 0` and `store.justified_checkpoint.epoch == 3`
-    # Skip epoch 0
-    next_epoch(spec, state)
-
-    # Forking another_state
-    another_state = state.copy()
-
-    # Fill epoch 1 with previous epoch attestations
-    _, signed_blocks, state = next_epoch_with_attestations(spec, state, False, True)
-    for block in signed_blocks:
-        spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-        run_on_block(spec, store, block)
-    # Skip epoch 2
-    next_epoch(spec, state)
-    # Fill epoch 3 & 4 with previous epoch attestations
-    for _ in range(2):
-        _, signed_blocks, state = next_epoch_with_attestations(spec, state, False, True)
-        for block in signed_blocks:
-            spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-            run_on_block(spec, store, block)
-
-    assert state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 0
-    assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
-    assert store.justified_checkpoint.hash_tree_root() == state.current_justified_checkpoint.hash_tree_root()
-
-    # Create another chain
-    # Goal: make `another_state.finalized_checkpoint.epoch == 2` and `another_state.justified_checkpoint.epoch == 3`
-    all_blocks = []
-    # Fill epoch 1 & 2 with previous + current epoch attestations
-    for _ in range(3):
-        _, signed_blocks, another_state = next_epoch_with_attestations(spec, another_state, True, True)
-        all_blocks += signed_blocks
-
-    assert another_state.finalized_checkpoint.epoch == 2
-    assert another_state.current_justified_checkpoint.epoch == 3
-    assert state.finalized_checkpoint.hash_tree_root() != another_state.finalized_checkpoint.hash_tree_root()
-    assert (
-        state.current_justified_checkpoint.hash_tree_root()
-        != another_state.current_justified_checkpoint.hash_tree_root()
-    )
-    pre_store_justified_checkpoint_root = store.justified_checkpoint.root
-
-    # Apply blocks of `another_state` to `store`
-    for block in all_blocks:
-        # NOTE: Do not call `on_tick` here
-        run_on_block(spec, store, block)
-
-    finalized_slot = spec.compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
-    ancestor_at_finalized_slot = spec.get_ancestor(store, pre_store_justified_checkpoint_root, finalized_slot)
-    assert ancestor_at_finalized_slot != store.finalized_checkpoint.root
-
-    assert store.finalized_checkpoint.hash_tree_root() == another_state.finalized_checkpoint.hash_tree_root()
-    assert store.justified_checkpoint.hash_tree_root() == another_state.current_justified_checkpoint.hash_tree_root()
-
-
-@with_all_phases
-@spec_state_test
-def test_new_finalized_slot_is_justified_checkpoint_ancestor(spec, state):
-    """
-    J: Justified
-    F: Finalized
-    state:
-        epoch
-        [0] <- [1] <- [2] <- [3] <- [4] <- [5]
-                       F             J
-
-    another_state (forked from state at epoch 3):
-                              └──── [4] <- [5]
-                              F      J
-    """
-    # Initialization
-    store = get_genesis_forkchoice_store(spec, state)
-
-    # Process state
-    next_epoch(spec, state)
-    spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-    _, signed_blocks, state = next_epoch_with_attestations(spec, state, False, True)
-    for block in signed_blocks:
-        spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-        run_on_block(spec, store, block)
-    _, signed_blocks, state = next_epoch_with_attestations(spec, state, True, False)
-    for block in signed_blocks:
-        spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-        run_on_block(spec, store, block)
-    next_epoch(spec, state)
-    spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-    for _ in range(2):
-        _, signed_blocks, state = next_epoch_with_attestations(spec, state, False, True)
-        for block in signed_blocks:
-            spec.on_tick(store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT)
-            run_on_block(spec, store, block)
-
-    assert state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 2
-    assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 4
-    assert store.justified_checkpoint.hash_tree_root() == state.current_justified_checkpoint.hash_tree_root()
-
-    # Create another chain
-    # Forking from epoch 3
-    all_blocks = []
-    slot = spec.compute_start_slot_at_epoch(3)
-    block_root = spec.get_block_root_at_slot(state, slot)
-    another_state = store.block_states[block_root].copy()
-    for _ in range(2):
-        _, signed_blocks, another_state = next_epoch_with_attestations(spec, another_state, True, True)
-        all_blocks += signed_blocks
-
-    assert another_state.finalized_checkpoint.epoch == 3
-    assert another_state.current_justified_checkpoint.epoch == 4
-
-    pre_store_justified_checkpoint_root = store.justified_checkpoint.root
-    for block in all_blocks:
-        if store.time < spec.compute_time_at_slot(another_state, block.message.slot):
-            spec.on_tick(store, store.genesis_time + block.message.slot * spec.config.SECONDS_PER_SLOT)
-        run_on_block(spec, store, block)
-
-    finalized_slot = spec.compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
-    ancestor_at_finalized_slot = spec.get_ancestor(store, pre_store_justified_checkpoint_root, finalized_slot)
-    assert ancestor_at_finalized_slot == store.finalized_checkpoint.root
-
-    assert store.finalized_checkpoint.hash_tree_root() == another_state.finalized_checkpoint.hash_tree_root()
-    assert store.justified_checkpoint.hash_tree_root() != another_state.current_justified_checkpoint.hash_tree_root()