Add additional get_proposer_head test coverage

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

@@ -65,6 +65,100 @@ def test_basic_is_head_root(spec, state):
     yield 'steps', test_steps
 
 
+@with_altair_and_later
+@spec_state_test
+def test_parent_weak(spec, state):
+    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
+
+    next_epoch(spec, state)
+    on_tick_and_append_step(spec, store, store.genesis_time + state.slot * spec.config.SECONDS_PER_SLOT, test_steps)
+
+    # Fill epoch 1 to 3
+    for _ in range(3):
+        state, store, _ = yield from apply_next_epoch_with_attestations(
+            spec, state, store, True, True, test_steps=test_steps)
+
+    assert spec.compute_epoch_at_slot(spec.get_current_slot(store)) == 4
+    assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
+    assert state.finalized_checkpoint.epoch == store.finalized_checkpoint.epoch == 2
+
+    # Make an empty block
+    block = build_empty_block_for_next_slot(spec, state)
+    signed_block = state_transition_and_sign_block(spec, state, block)
+    yield from tick_and_add_block(spec, store, signed_block, test_steps)
+
+    # Fill a slot (parent)
+    state, store, signed_parent_block = yield from apply_next_slots_with_attestations(
+        spec, state, store, 1, True, True, test_steps)
+
+    block = build_empty_block_for_next_slot(spec, state)
+    signed_block = state_transition_and_sign_block(spec, state, block)
+
+    # Make the head block late
+    attesting_cutoff = spec.config.SECONDS_PER_SLOT // spec.INTERVALS_PER_SLOT
+    current_time = state.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time + attesting_cutoff
+    on_tick_and_append_step(spec, store, current_time, test_steps)
+    assert store.time == current_time
+
+    yield from tick_and_add_block(spec, store, signed_block, test_steps)
+
+    # Check conditions
+    head_root = spec.get_head(store)
+    head_block = store.blocks[head_root]
+    parent_root = head_block.parent_root
+    assert parent_root == signed_parent_block.message.hash_tree_root()
+    parent_block = store.blocks[parent_root]
+
+    # Proposing next slot
+    next_slot(spec, state)
+    slot = state.slot
+
+    # Add attestations to the parent block
+    attestations = get_valid_attestation_at_slot(
+        state,
+        spec,
+        slot_to_attest=slot - 1,
+        beacon_block_root=parent_root,
+    )
+    for attestation in attestations:
+        yield from tick_and_run_on_attestation(spec, store, attestation, test_steps)
+
+    # The conditions in `get_proposer_head`
+    assert spec.is_head_late(store, head_root)
+    assert spec.is_shuffling_stable(slot)
+    assert spec.is_ffg_competitive(store, head_root, parent_root)
+    assert spec.is_finalization_ok(store, slot)
+    assert spec.is_proposing_on_time(store)
+
+    parent_slot_ok = parent_block.slot + 1 == head_block.slot
+    current_time_ok = head_block.slot + 1 == slot
+    single_slot_reorg = parent_slot_ok and current_time_ok
+    assert single_slot_reorg
+
+    assert spec.is_head_weak(store, head_root)
+    assert not spec.is_parent_strong(store, parent_root)
+
+    proposer_head = spec.get_proposer_head(store, head_root, state.slot)
+    assert proposer_head != parent_root
+    assert proposer_head == head_root
+
+    output_store_checks(spec, store, test_steps)
+    test_steps.append({
+        'checks': {
+            'get_proposer_head': encode_hex(proposer_head),
+        }
+    })
+
+    yield 'steps', test_steps
+
+
 @with_altair_and_later
 @spec_state_test
 def test_basic_is_parent_root(spec, state):