Add test verifying zero-amount pending withdrawal is correctly processed

[bshastry]

Adds a new test called test_pending_withdrawal_amount_zero_ineffective_sweep to verify:

• Processing of zero-amount pending withdrawals
• Interaction with sweep eligibility
• State cleanup after processing

[jtraglia]

Hey @bshastry, a zero-amount withdrawal isn't a possible situation.

See here, a zero-amount withdrawal request is considered a full exit:

consensus-specs/specs/electra/beacon-chain.md

Lines 1511 to 1516 in c84d1c4

	def process_withdrawal_request(
	state: BeaconState,
	withdrawal_request: WithdrawalRequest
	) -> None:
	amount = withdrawal_request.amount
	is_full_exit_request = amount == FULL_EXIT_REQUEST_AMOUNT

consensus-specs/specs/electra/beacon-chain.md

Line 136 in c84d1c4

| `FULL_EXIT_REQUEST_AMOUNT` | `uint64(0)` | *[New in Electra:EIP7002]* Withdrawal amount used to signal a full validator exit |

[bshastry]

Hey @bshastry, a zero-amount withdrawal isn't a possible situation.

See here, a zero-amount withdrawal request is considered a full exit:

consensus-specs/specs/electra/beacon-chain.md

Lines 1511 to 1516 in c84d1c4

	def process_withdrawal_request(
	state: BeaconState,
	withdrawal_request: WithdrawalRequest
	) -> None:
	amount = withdrawal_request.amount
	is_full_exit_request = amount == FULL_EXIT_REQUEST_AMOUNT

consensus-specs/specs/electra/beacon-chain.md

Line 136 in c84d1c4

| `FULL_EXIT_REQUEST_AMOUNT` | `uint64(0)` | *[New in Electra:EIP7002]* Withdrawal amount used to signal a full validator exit |

Thank you so much for pointing out. Well, I suppose that leaves us with three options (or potentially both)

1. Test for a full exit perhaps add an assertion that the validator exited after the zero-amount withdrawal was requested?
2. Test for the minimal non-zero amount e.g., 1, and assert that it was processed correctly
3. Add tests for both (1) and (2)

Wdyt?

[jtraglia]

Hey @bshastry, those are good test ideas but they already exist 😄

Test for a full exit perhaps add an assertion that the validator exited after the zero-amount withdrawal was requested?

consensus-specs/tests/core/pyspec/eth2spec/test/electra/block_processing/test_process_withdrawal_request.py

Lines 108 to 128 in 099919f

	def test_basic_withdrawal_request(spec, state):
	rng = random.Random(1337)
	# move state forward SHARD_COMMITTEE_PERIOD epochs to allow for exit
	state.slot += spec.config.SHARD_COMMITTEE_PERIOD * spec.SLOTS_PER_EPOCH
	current_epoch = spec.get_current_epoch(state)
	validator_index = rng.choice(spec.get_active_validator_indices(state, current_epoch))
	validator_pubkey = state.validators[validator_index].pubkey
	address = b"\x22" * 20
	set_eth1_withdrawal_credential_with_balance(
	spec, state, validator_index, address=address
	)
	withdrawal_request = spec.WithdrawalRequest(
	source_address=address,
	validator_pubkey=validator_pubkey,
	amount=spec.FULL_EXIT_REQUEST_AMOUNT,
	)
	yield from run_withdrawal_request_processing(
	spec, state, withdrawal_request
	)

The assertions are in the run_withdrawal_request_processing helper function:

consensus-specs/tests/core/pyspec/eth2spec/test/electra/block_processing/test_process_withdrawal_request.py

Lines 68 to 72 in 099919f

	if withdrawal_request.amount == spec.FULL_EXIT_REQUEST_AMOUNT:
	assert pre_exit_epoch == spec.FAR_FUTURE_EPOCH
	assert state.validators[validator_index].exit_epoch < spec.FAR_FUTURE_EPOCH
	assert spec.get_pending_balance_to_withdraw(state, validator_index) == 0
	assert state.pending_partial_withdrawals == pre_pending_partial_withdrawals

Test for the minimal non-zero amount e.g., 1, and assert that it was processed correctly

consensus-specs/tests/core/pyspec/eth2spec/test/electra/block_processing/test_process_withdrawal_request.py

Lines 609 to 636 in 099919f

	def test_partial_withdrawal_request_with_low_amount(spec, state):
	rng = random.Random(1351)
	state.slot += spec.config.SHARD_COMMITTEE_PERIOD * spec.SLOTS_PER_EPOCH
	current_epoch = spec.get_current_epoch(state)
	validator_index = rng.choice(spec.get_active_validator_indices(state, current_epoch))
	validator_pubkey = state.validators[validator_index].pubkey
	address = b"\x22" * 20
	amount = 1
	# Give the validator some excess balance to withdraw
	state.balances[validator_index] += amount
	set_compounding_withdrawal_credential(spec, state, validator_index, address=address)
	withdrawal_request = spec.WithdrawalRequest(
	source_address=address,
	validator_pubkey=validator_pubkey,
	amount=amount,
	)
	yield from run_withdrawal_request_processing(
	spec,
	state,
	withdrawal_request,
	)
	# Check that the assigned exit epoch is correct
	assert state.earliest_exit_epoch == spec.compute_activation_exit_epoch(
	current_epoch
	)

[bshastry]

Sorry for taking your time @jtraglia . I'm going to close this PR since the tests are already there.