Add invalid large withdrawable epoch test

tests/core/pyspec/eth2spec/test/phase0/epoch_processing/test_process_registry_updates.py

@@ -1,3 +1,5 @@
+import pytest
+
 from eth2spec.test.helpers.deposits import mock_deposit
 from eth2spec.test.helpers.state import next_epoch, next_slots
 from eth2spec.test.helpers.constants import MINIMAL
@@ -342,3 +344,27 @@ def test_activation_queue_activation_and_ejection__exceed_scaled_churn_limit(spe
     churn_limit = spec.get_validator_churn_limit(state)
     assert churn_limit > spec.config.MIN_PER_EPOCH_CHURN_LIMIT
     yield from run_test_activation_queue_activation_and_ejection(spec, state, churn_limit * 2)
+
+
+@with_all_phases
+@spec_state_test
+def test_invalid_large_withdrawable_epoch(spec, state):
+    """
+    This test forces a validator into a withdrawable epoch that overflows the
+    epoch (uint64) type. To do this we need two validators, one validator that
+    already has an exit epoch and another with a low effective balance. When
+    calculating the withdrawable epoch for the second validator, it will
+    use the greatest exit epoch of all of the validators. If the first
+    validator is given an exit epoch between
+    (FAR_FUTURE_EPOCH-MIN_VALIDATOR_WITHDRAWABILITY_DELAY+1) and
+    (FAR_FUTURE_EPOCH-1), it will cause an overflow.
+    """
+    assert spec.is_active_validator(state.validators[0], spec.get_current_epoch(state))
+    assert spec.is_active_validator(state.validators[1], spec.get_current_epoch(state))
+
+    state.validators[0].exit_epoch = spec.FAR_FUTURE_EPOCH - 1
+    state.validators[1].effective_balance = spec.config.EJECTION_BALANCE
+
+    with pytest.raises(ValueError):
+        yield from run_process_registry_updates(spec, state)
+    yield 'post', None