diff --git a/specs/phase0/fork-choice.md b/specs/phase0/fork-choice.md
index d3b0e2dc5..de0a2e785 100644
--- a/specs/phase0/fork-choice.md
+++ b/specs/phase0/fork-choice.md
@@ -267,6 +267,7 @@ def get_head(store: Store) -> Root:
         if len(children) == 0:
             return head
         # Sort by latest attesting balance with ties broken lexicographically
+        # Ties broken by favoring block with lexicographically higher root
         head = max(children, key=lambda root: (get_latest_attesting_balance(store, root), root))
 ```
 
diff --git a/tests/core/pyspec/eth2spec/test/context.py b/tests/core/pyspec/eth2spec/test/context.py
index 184c0d609..260cb4d7d 100644
--- a/tests/core/pyspec/eth2spec/test/context.py
+++ b/tests/core/pyspec/eth2spec/test/context.py
@@ -1,6 +1,7 @@
 import pytest
-from copy import deepcopy
 from dataclasses import dataclass
+import importlib
+from eth_utils import encode_hex
 
 from eth2spec.phase0 import mainnet as spec_phase0_mainnet, minimal as spec_phase0_minimal
 from eth2spec.altair import mainnet as spec_altair_mainnet, minimal as spec_altair_minimal
@@ -85,10 +86,9 @@ class SpecForks(TypedDict, total=False):
 
 def _prepare_state(balances_fn: Callable[[Any], Sequence[int]], threshold_fn: Callable[[Any], int],
                    spec: Spec, phases: SpecForks):
-    phase = phases[spec.fork]
-    balances = balances_fn(phase)
-    activation_threshold = threshold_fn(phase)
-    state = create_genesis_state(spec=phase, validator_balances=balances,
+    balances = balances_fn(spec)
+    activation_threshold = threshold_fn(spec)
+    state = create_genesis_state(spec=spec, validator_balances=balances,
                                  activation_threshold=activation_threshold)
     return state
 
@@ -464,6 +464,32 @@ def with_presets(preset_bases, reason=None):
     return decorator
 
 
+def _get_basic_dict(ssz_dict: Dict[str, Any]) -> Dict[str, Any]:
+    """
+    Get dict of Python built-in types from a dict of SSZ objects.
+    """
+    result = {}
+    for k, v in ssz_dict.items():
+        if isinstance(v, int):
+            value = int(v)
+        elif isinstance(v, bytes):
+            value = encode_hex(v)
+        else:
+            value = str(v)
+        result[k] = value
+    return result
+
+
+def _get_copy_of_spec(spec):
+    fork = spec.fork
+    preset = spec.config.PRESET_BASE
+    module_path = f"eth2spec.{fork}.{preset}"
+    module_spec = importlib.util.find_spec(module_path)
+    module = importlib.util.module_from_spec(module_spec)
+    module_spec.loader.exec_module(module)
+    return module
+
+
 def with_config_overrides(config_overrides):
     """
     WARNING: the spec_test decorator must wrap this, to ensure the decorated test actually runs.
@@ -474,20 +500,20 @@ def with_config_overrides(config_overrides):
     """
     def decorator(fn):
         def wrapper(*args, spec: Spec, **kw):
-            # remember the old config
-            old_config = spec.config
+            spec = _get_copy_of_spec(spec)
 
             # apply our overrides to a copy of it, and apply it to the spec
-            tmp_config = deepcopy(old_config._asdict())  # not a private method, there are multiple
-            tmp_config.update(config_overrides)
+            config = spec.config._asdict()
+            config.update(config_overrides)
             config_types = spec.Configuration.__annotations__
-            # Retain types of all config values
-            test_config = {k: config_types[k](v) for k, v in tmp_config.items()}
+            modified_config = {k: config_types[k](v) for k, v in config.items()}
 
-            # Output the config for test vectors  (TODO: check config YAML encoding)
-            yield 'config', 'data', test_config
+            # To output the changed config to could be serialized with yaml test vectors,
+            # the dict SSZ objects have to be converted into Python built-in types.
+            output_config = _get_basic_dict(modified_config)
+            yield 'config', 'data', output_config
 
-            spec.config = spec.Configuration(**test_config)
+            spec.config = spec.Configuration(**modified_config)
 
             # Run the function
             out = fn(*args, spec=spec, **kw)
@@ -495,10 +521,6 @@ def with_config_overrides(config_overrides):
             # it's generating things, and we need to complete it before setting back the config.
             if out is not None:
                 yield from out
-
-            # Restore the old config and apply it
-            spec.config = old_config
-
         return wrapper
     return decorator
 
diff --git a/tests/core/pyspec/eth2spec/test/helpers/fork_choice.py b/tests/core/pyspec/eth2spec/test/helpers/fork_choice.py
index 0b06f283f..f056b9acd 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/fork_choice.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/fork_choice.py
@@ -42,6 +42,12 @@ def tick_and_add_block(spec, store, signed_block, test_steps, valid=True,
     return post_state
 
 
+def add_attestation(spec, store, attestation, test_steps, is_from_block=False):
+    spec.on_attestation(store, attestation, is_from_block=is_from_block)
+    yield get_attestation_file_name(attestation), attestation
+    test_steps.append({'attestation': get_attestation_file_name(attestation)})
+
+
 def tick_and_run_on_attestation(spec, store, attestation, test_steps, is_from_block=False):
     parent_block = store.blocks[attestation.data.beacon_block_root]
     pre_state = store.block_states[spec.hash_tree_root(parent_block)]
@@ -52,9 +58,7 @@ def tick_and_run_on_attestation(spec, store, attestation, test_steps, is_from_bl
         spec.on_tick(store, next_epoch_time)
         test_steps.append({'tick': int(next_epoch_time)})
 
-    spec.on_attestation(store, attestation, is_from_block=is_from_block)
-    yield get_attestation_file_name(attestation), attestation
-    test_steps.append({'attestation': get_attestation_file_name(attestation)})
+    yield from add_attestation(spec, store, attestation, test_steps, is_from_block)
 
 
 def run_on_attestation(spec, store, attestation, is_from_block=False, valid=True):
diff --git a/tests/core/pyspec/eth2spec/test/phase0/fork_choice/test_ex_ante.py b/tests/core/pyspec/eth2spec/test/phase0/fork_choice/test_ex_ante.py
new file mode 100644
index 000000000..d93101156
--- /dev/null
+++ b/tests/core/pyspec/eth2spec/test/phase0/fork_choice/test_ex_ante.py
@@ -0,0 +1,421 @@
+from eth2spec.test.context import (
+    MAINNET,
+    spec_state_test,
+    with_all_phases,
+    with_presets,
+)
+from eth2spec.test.helpers.attestations import (
+    get_valid_attestation,
+    sign_attestation,
+)
+from eth2spec.test.helpers.block import (
+    build_empty_block,
+)
+from eth2spec.test.helpers.fork_choice import (
+    get_genesis_forkchoice_store_and_block,
+    on_tick_and_append_step,
+    add_attestation,
+    add_block,
+    tick_and_add_block,
+)
+from eth2spec.test.helpers.state import (
+    state_transition_and_sign_block,
+)
+
+
+def _apply_base_block_a(spec, state, store, test_steps):
+    # On receiving block A at slot `N`
+    block = build_empty_block(spec, state, slot=state.slot + 1)
+    signed_block_a = state_transition_and_sign_block(spec, state, block)
+    yield from tick_and_add_block(spec, store, signed_block_a, test_steps)
+    assert spec.get_head(store) == signed_block_a.message.hash_tree_root()
+
+
+@with_all_phases
+@spec_state_test
+def test_ex_ante_vanilla(spec, state):
+    """
+    With a single adversarial attestation
+    Objects:
+        Block A - slot N
+        Block B (parent A) - slot N+1
+        Block C (parent A) - slot N+2
+        Attestation_1 (Block B); size `1` - slot N+1
+    Steps:
+        Block A received at N — A is head
+        Block C received at N+2 — C is head
+        Block B received at N+2 — C is head
+        Attestation_1 received at N+2 — C is head
+    """
+    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
+
+    # On receiving block A at slot `N`
+    yield from _apply_base_block_a(spec, state, store, test_steps)
+    state_a = state.copy()
+
+    # Block B at slot `N + 1`, parent is A
+    state_b = state_a.copy()
+    block = build_empty_block(spec, state_a, slot=state_a.slot + 1)
+    signed_block_b = state_transition_and_sign_block(spec, state_b, block)
+
+    # Block C at slot `N + 2`, parent is A
+    state_c = state_a.copy()
+    block = build_empty_block(spec, state_c, slot=state_a.slot + 2)
+    signed_block_c = state_transition_and_sign_block(spec, state_c, block)
+
+    # Attestation_1 at slot `N + 1` voting for block B
+    def _filter_participant_set(participants):
+        return [next(iter(participants))]
+
+    attestation = get_valid_attestation(
+        spec, state_b, slot=state_b.slot, signed=False, filter_participant_set=_filter_participant_set
+    )
+    attestation.data.beacon_block_root = signed_block_b.message.hash_tree_root()
+    assert len([i for i in attestation.aggregation_bits if i == 1]) == 1
+    sign_attestation(spec, state_b, attestation)
+
+    # Block C received at N+2 — C is head
+    time = state_c.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, time, test_steps)
+    yield from add_block(spec, store, signed_block_c, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Block B received at N+2 — C is head due to proposer score boost
+    yield from add_block(spec, store, signed_block_b, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Attestation_1 received at N+2 — C is head
+    yield from add_attestation(spec, store, attestation, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    yield 'steps', test_steps
+
+
+def _get_greater_than_proposer_boost_score(spec, store, state, proposer_boost_root, root):
+    """
+    Return the minimum attestation participant count such that attestation_score > proposer_score
+    """
+    # calculate proposer boost score
+    block = store.blocks[root]
+    proposer_score = 0
+    if spec.get_ancestor(store, root, block.slot) == proposer_boost_root:
+        num_validators = len(spec.get_active_validator_indices(state, spec.get_current_epoch(state)))
+        avg_balance = spec.get_total_active_balance(state) // num_validators
+        committee_size = num_validators // spec.SLOTS_PER_EPOCH
+        committee_weight = committee_size * avg_balance
+        proposer_score = (committee_weight * spec.config.PROPOSER_SCORE_BOOST) // 100
+
+    # calculate minimum participant count such that attestation_score > proposer_score
+    base_effective_balance = state.validators[0].effective_balance
+
+    return proposer_score // base_effective_balance + 1
+
+
+@with_all_phases
+@with_presets([MAINNET], reason="to create non-duplicate committee")
+@spec_state_test
+def test_ex_ante_attestations_is_greater_than_proposer_boost_with_boost(spec, state):
+    """
+    Adversarial attestations > proposer boost
+    Objects:
+        Block A - slot N
+        Block B (parent A) - slot N+1
+        Block C (parent A) - slot N+2
+        Attestation_set_1 (Block B); size `proposer_boost + 1` - slot N+1
+    Steps:
+        Block A received at N — A is head
+        Block C received at N+2 — C is head
+        Block B received at N+2 — C is head
+        Attestation_1 received at N+2 — B is head
+    """
+    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
+
+    # On receiving block A at slot `N`
+    yield from _apply_base_block_a(spec, state, store, test_steps)
+    state_a = state.copy()
+
+    # Block B at slot `N + 1`, parent is A
+    state_b = state_a.copy()
+    block = build_empty_block(spec, state_a, slot=state_a.slot + 1)
+    signed_block_b = state_transition_and_sign_block(spec, state_b, block)
+
+    # Block C at slot `N + 2`, parent is A
+    state_c = state_a.copy()
+    block = build_empty_block(spec, state_c, slot=state_a.slot + 2)
+    signed_block_c = state_transition_and_sign_block(spec, state_c, block)
+
+    # Block C received at N+2 — C is head
+    time = state_c.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, time, test_steps)
+    yield from add_block(spec, store, signed_block_c, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Block B received at N+2 — C is head due to proposer score boost
+    yield from add_block(spec, store, signed_block_b, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Attestation_set_1 at slot `N + 1` voting for block B
+    proposer_boost_root = signed_block_b.message.hash_tree_root()
+    root = signed_block_b.message.hash_tree_root()
+    participant_num = _get_greater_than_proposer_boost_score(spec, store, state, proposer_boost_root, root)
+
+    def _filter_participant_set(participants):
+        return [index for i, index in enumerate(participants) if i < participant_num]
+
+    attestation = get_valid_attestation(
+        spec, state_b, slot=state_b.slot, signed=False, filter_participant_set=_filter_participant_set
+    )
+    attestation.data.beacon_block_root = signed_block_b.message.hash_tree_root()
+    assert len([i for i in attestation.aggregation_bits if i == 1]) == participant_num
+    sign_attestation(spec, state_b, attestation)
+
+    # Attestation_set_1 received at N+2 — B is head because B's attestation_score > C's proposer_score.
+    # (B's proposer_score = C's attestation_score = 0)
+    yield from add_attestation(spec, store, attestation, test_steps)
+    assert spec.get_head(store) == signed_block_b.message.hash_tree_root()
+
+    yield 'steps', test_steps
+
+
+@with_all_phases
+@spec_state_test
+def test_ex_ante_sandwich_without_attestations(spec, state):
+    """
+    Simple Sandwich test with boost and no attestations.
+    Obejcts:
+        Block A - slot N
+        Block B (parent A) - slot N+1
+        Block C (parent A) - slot N+2
+        Block D (parent B) - slot N+3
+    Steps:
+        Block A received at N — A is head
+        Block C received at N+2 — C is head
+        Block B received at N+2 — C is head (with boost)
+        Block D received at N+3 — D is head (with boost)
+    """
+    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
+
+    # On receiving block A at slot `N`
+    yield from _apply_base_block_a(spec, state, store, test_steps)
+    state_a = state.copy()
+
+    # Block B at slot `N + 1`, parent is A
+    state_b = state_a.copy()
+    block = build_empty_block(spec, state_a, slot=state_a.slot + 1)
+    signed_block_b = state_transition_and_sign_block(spec, state_b, block)
+
+    # Block C at slot `N + 2`, parent is A
+    state_c = state_a.copy()
+    block = build_empty_block(spec, state_c, slot=state_a.slot + 2)
+    signed_block_c = state_transition_and_sign_block(spec, state_c, block)
+
+    # Block D at slot `N + 3`, parent is B
+    state_d = state_b.copy()
+    block = build_empty_block(spec, state_d, slot=state_a.slot + 3)
+    signed_block_d = state_transition_and_sign_block(spec, state_d, block)
+
+    # Block C received at N+2 — C is head
+    time = state_c.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, time, test_steps)
+    yield from add_block(spec, store, signed_block_c, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Block B received at N+2 — C is head, it has proposer score boost
+    yield from add_block(spec, store, signed_block_b, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Block D received at N+3 - D is head, it has proposer score boost
+    time = state_d.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, time, test_steps)
+    yield from add_block(spec, store, signed_block_d, test_steps)
+    assert spec.get_head(store) == signed_block_d.message.hash_tree_root()
+
+    yield 'steps', test_steps
+
+
+@with_all_phases
+@spec_state_test
+def test_ex_ante_sandwich_with_honest_attestation(spec, state):
+    """
+    Boosting necessary to sandwich attack.
+    Objects:
+        Block A - slot N
+        Block B (parent A) - slot N+1
+        Block C (parent A) - slot N+2
+        Block D (parent B) - slot N+3
+        Attestation_1 (Block C); size 1 - slot N+2 (honest)
+    Steps:
+        Block A received at N — A is head
+        Block C received at N+2 — C is head
+        Block B received at N+2 — C is head
+        Attestation_1 received at N+3 — C is head
+        Block D received at N+3 — D is head
+
+    """
+    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
+
+    # On receiving block A at slot `N`
+    yield from _apply_base_block_a(spec, state, store, test_steps)
+    state_a = state.copy()
+
+    # Block B at slot `N + 1`, parent is A
+    state_b = state_a.copy()
+    block = build_empty_block(spec, state_a, slot=state_a.slot + 1)
+    signed_block_b = state_transition_and_sign_block(spec, state_b, block)
+
+    # Block C at slot `N + 2`, parent is A
+    state_c = state_a.copy()
+    block = build_empty_block(spec, state_c, slot=state_a.slot + 2)
+    signed_block_c = state_transition_and_sign_block(spec, state_c, block)
+
+    # Attestation_1 at N+2 voting for block C
+    def _filter_participant_set(participants):
+        return [next(iter(participants))]
+
+    attestation = get_valid_attestation(
+        spec, state_c, slot=state_c.slot, signed=False, filter_participant_set=_filter_participant_set
+    )
+    attestation.data.beacon_block_root = signed_block_c.message.hash_tree_root()
+    assert len([i for i in attestation.aggregation_bits if i == 1]) == 1
+    sign_attestation(spec, state_c, attestation)
+
+    # Block D at slot `N + 3`, parent is B
+    state_d = state_b.copy()
+    block = build_empty_block(spec, state_d, slot=state_a.slot + 3)
+    signed_block_d = state_transition_and_sign_block(spec, state_d, block)
+
+    # Block C received at N+2 — C is head
+    time = state_c.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, time, test_steps)
+    yield from add_block(spec, store, signed_block_c, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Block B received at N+2 — C is head, it has proposer score boost
+    yield from add_block(spec, store, signed_block_b, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Attestation_1 received at N+3 — C is head
+    time = state_d.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, time, test_steps)
+    yield from add_attestation(spec, store, attestation, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Block D received at N+3 - D is head, it has proposer score boost
+    yield from add_block(spec, store, signed_block_d, test_steps)
+    assert spec.get_head(store) == signed_block_d.message.hash_tree_root()
+
+    yield 'steps', test_steps
+
+
+@with_all_phases
+@with_presets([MAINNET], reason="to create non-duplicate committee")
+@spec_state_test
+def test_ex_ante_sandwich_with_boost_not_sufficient(spec, state):
+    """
+    Boost not sufficient to sandwich attack.
+    Objects:
+        Block A - slot N
+        Block B (parent A) - slot N+1
+        Block C (parent A) - slot N+2
+        Block D (parent B) - slot N+3
+        Attestation_set_1 (Block C); size proposer_boost + 1 - slot N+2
+    Steps:
+        Block A received at N — A is head
+        Block C received at N+2 — C is head
+        Block B received at N+2 — C is head
+        Attestation_set_1 received — C is head
+        Block D received at N+3 — C is head
+    """
+    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
+
+    # On receiving block A at slot `N`
+    yield from _apply_base_block_a(spec, state, store, test_steps)
+    state_a = state.copy()
+
+    # Block B at slot `N + 1`, parent is A
+    state_b = state_a.copy()
+    block = build_empty_block(spec, state_a, slot=state_a.slot + 1)
+    signed_block_b = state_transition_and_sign_block(spec, state_b, block)
+
+    # Block C at slot `N + 2`, parent is A
+    state_c = state_a.copy()
+    block = build_empty_block(spec, state_c, slot=state_a.slot + 2)
+    signed_block_c = state_transition_and_sign_block(spec, state_c, block)
+
+    # Block D at slot `N + 3`, parent is B
+    state_d = state_b.copy()
+    block = build_empty_block(spec, state_d, slot=state_a.slot + 3)
+    signed_block_d = state_transition_and_sign_block(spec, state_d, block)
+
+    # Block C received at N+2 — C is head
+    time = state_c.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, time, test_steps)
+    yield from add_block(spec, store, signed_block_c, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Block B received at N+2 — C is head, it has proposer score boost
+    yield from add_block(spec, store, signed_block_b, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Attestation_set_1 at N+2 voting for block C
+    proposer_boost_root = signed_block_c.message.hash_tree_root()
+    root = signed_block_c.message.hash_tree_root()
+    participant_num = _get_greater_than_proposer_boost_score(spec, store, state, proposer_boost_root, root)
+
+    def _filter_participant_set(participants):
+        return [index for i, index in enumerate(participants) if i < participant_num]
+
+    attestation = get_valid_attestation(
+        spec, state_c, slot=state_c.slot, signed=False, filter_participant_set=_filter_participant_set
+    )
+    attestation.data.beacon_block_root = signed_block_c.message.hash_tree_root()
+    assert len([i for i in attestation.aggregation_bits if i == 1]) == participant_num
+    sign_attestation(spec, state_c, attestation)
+
+    # Attestation_1 received at N+3 — B is head because B's attestation_score > C's proposer_score.
+    # (B's proposer_score = C's attestation_score = 0)
+    time = state_d.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, time, test_steps)
+    yield from add_attestation(spec, store, attestation, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    # Block D received at N+3 - C is head, D's boost not sufficient!
+    yield from add_block(spec, store, signed_block_d, test_steps)
+    assert spec.get_head(store) == signed_block_c.message.hash_tree_root()
+
+    yield 'steps', test_steps
diff --git a/tests/generators/fork_choice/main.py b/tests/generators/fork_choice/main.py
index 562f851d1..b194dc3bd 100644
--- a/tests/generators/fork_choice/main.py
+++ b/tests/generators/fork_choice/main.py
@@ -6,6 +6,7 @@ if __name__ == "__main__":
     phase_0_mods = {key: 'eth2spec.test.phase0.fork_choice.test_' + key for key in [
         'get_head',
         'on_block',
+        'ex_ante',
     ]}
     # No additional Altair specific finality tests, yet.
     altair_mods = phase_0_mods