add larger validator set test for regression test for active_shard_count issue

specs/phase1/beacon-chain.md

@@ -47,6 +47,7 @@
     - [`compute_updated_gasprice`](#compute_updated_gasprice)
     - [`compute_committee_source_epoch`](#compute_committee_source_epoch)
   - [Beacon state accessors](#beacon-state-accessors)
+    - [New `get_committee_count_per_slot`](#new-get_committee_count_per_slot)
     - [`get_active_shard_count`](#get_active_shard_count)
     - [`get_online_validator_indices`](#get_online_validator_indices)
     - [`get_shard_committee`](#get_shard_committee)

tests/core/pyspec/eth2spec/test/context.py

@@ -151,6 +151,15 @@ def low_single_balance(spec):
     return [1]
 
 
+def large_validator_set(spec):
+    """
+    Helper method to create a series of default balances.
+    Usage: `@with_custom_state(balances_fn=default_balances, ...)`
+    """
+    num_validators = 2 * spec.SLOTS_PER_EPOCH * spec.MAX_COMMITTEES_PER_SLOT * spec.TARGET_COMMITTEE_SIZE
+    return [spec.MAX_EFFECTIVE_BALANCE] * num_validators
+
+
 def single_phase(fn):
     """
     Decorator that filters out the phases data.

tests/core/pyspec/eth2spec/test/phase0/sanity/test_blocks.py

@@ -22,7 +22,10 @@ from eth2spec.test.helpers.shard_transitions import get_shard_transition_of_comm
 
 from eth2spec.test.context import (
     PHASE0, PHASE1,
+    spec_test,
     spec_state_test, with_all_phases, expect_assertion_error, always_bls, with_phases,
+    with_custom_state, single_phase,
+    large_validator_set,
 )
 
 
@@ -85,6 +88,28 @@ def test_empty_block_transition(spec, state):
     assert spec.get_randao_mix(state, spec.get_current_epoch(state)) != spec.Bytes32()
 
 
+@with_all_phases
+@spec_test
+@with_custom_state(balances_fn=large_validator_set, threshold_fn=lambda spec: spec.EJECTION_BALANCE)
+@single_phase
+def test_empty_block_transition_large_validator_set(spec, state):
+    pre_slot = state.slot
+    pre_eth1_votes = len(state.eth1_data_votes)
+
+    yield 'pre', state
+
+    block = build_empty_block_for_next_slot(spec, state)
+
+    signed_block = state_transition_and_sign_block(spec, state, block)
+
+    yield 'blocks', [signed_block]
+    yield 'post', state
+
+    assert len(state.eth1_data_votes) == pre_eth1_votes + 1
+    assert spec.get_block_root_at_slot(state, pre_slot) == signed_block.message.parent_root
+    assert spec.get_randao_mix(state, spec.get_current_epoch(state)) != spec.Bytes32()
+
+
 def process_and_sign_block_without_header_validations(spec, state, block):
     """
     Artificially bypass the restrictions in the state transition to transition and sign block
@@ -288,6 +313,26 @@ def test_empty_epoch_transition(spec, state):
         assert spec.get_block_root_at_slot(state, slot) == block.parent_root
 
 
+@with_all_phases
+@spec_test
+@with_custom_state(balances_fn=large_validator_set, threshold_fn=lambda spec: spec.EJECTION_BALANCE)
+@single_phase
+def test_empty_epoch_transition_large_validator_set(spec, state):
+    pre_slot = state.slot
+    yield 'pre', state
+
+    block = build_empty_block(spec, state, state.slot + spec.SLOTS_PER_EPOCH)
+
+    signed_block = state_transition_and_sign_block(spec, state, block)
+
+    yield 'blocks', [signed_block]
+    yield 'post', state
+
+    assert state.slot == block.slot
+    for slot in range(pre_slot, state.slot):
+        assert spec.get_block_root_at_slot(state, slot) == block.parent_root
+
+
 @with_all_phases
 @spec_state_test
 def test_empty_epoch_transition_not_finalizing(spec, state):