eth2.0-specs/test_libs/pyspec/eth2spec/test/test_finality.py

from eth2spec.test.context import spec_state_test, never_bls, with_all_phases
from eth2spec.test.helpers.state import next_epoch, next_epoch_with_attestations
from eth2spec.test.helpers.block import apply_empty_block


def check_finality(spec,
                   state,
                   prev_state,
                   current_justified_changed,
                   previous_justified_changed,
                   finalized_changed):
    if current_justified_changed:
        assert state.current_justified_checkpoint.epoch > prev_state.current_justified_checkpoint.epoch
        assert state.current_justified_checkpoint.root != prev_state.current_justified_checkpoint.root
    else:
        assert state.current_justified_checkpoint == prev_state.current_justified_checkpoint

    if previous_justified_changed:
        assert state.previous_justified_checkpoint.epoch > prev_state.previous_justified_checkpoint.epoch
        assert state.previous_justified_checkpoint.root != prev_state.previous_justified_checkpoint.root
    else:
        assert state.previous_justified_checkpoint == prev_state.previous_justified_checkpoint

    if finalized_changed:
        assert state.finalized_checkpoint.epoch > prev_state.finalized_checkpoint.epoch
        assert state.finalized_checkpoint.root != prev_state.finalized_checkpoint.root
    else:
        assert state.finalized_checkpoint == prev_state.finalized_checkpoint


@with_all_phases
@never_bls
@spec_state_test
def test_finality_no_updates_at_genesis(spec, state):
    assert spec.get_current_epoch(state) == spec.GENESIS_EPOCH

    yield 'pre', state

    blocks = []
    for epoch in range(2):
        prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, True, False)
        blocks += new_blocks

        # justification/finalization skipped at GENESIS_EPOCH
        if epoch == 0:
            check_finality(spec, state, prev_state, False, False, False)
        # justification/finalization skipped at GENESIS_EPOCH + 1
        elif epoch == 1:
            check_finality(spec, state, prev_state, False, False, False)

    yield 'blocks', blocks
    yield 'post', state


@with_all_phases
@never_bls
@spec_state_test
def test_finality_rule_4(spec, state):
    # get past first two epochs that finality does not run on
    next_epoch(spec, state)
    apply_empty_block(spec, state)
    next_epoch(spec, state)
    apply_empty_block(spec, state)

    yield 'pre', state

    blocks = []
    for epoch in range(2):
        prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, True, False)
        blocks += new_blocks

        if epoch == 0:
            check_finality(spec, state, prev_state, True, False, False)
        elif epoch == 1:
            # rule 4 of finality
            check_finality(spec, state, prev_state, True, True, True)
            assert state.finalized_checkpoint == prev_state.current_justified_checkpoint

    yield 'blocks', blocks
    yield 'post', state


@with_all_phases
@never_bls
@spec_state_test
def test_finality_rule_1(spec, state):
    # get past first two epochs that finality does not run on
    next_epoch(spec, state)
    apply_empty_block(spec, state)
    next_epoch(spec, state)
    apply_empty_block(spec, state)

    yield 'pre', state

    blocks = []
    for epoch in range(3):
        prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, False, True)
        blocks += new_blocks

        if epoch == 0:
            check_finality(spec, state, prev_state, True, False, False)
        elif epoch == 1:
            check_finality(spec, state, prev_state, True, True, False)
        elif epoch == 2:
            # finalized by rule 1
            check_finality(spec, state, prev_state, True, True, True)
            assert state.finalized_checkpoint == prev_state.previous_justified_checkpoint

    yield 'blocks', blocks
    yield 'post', state


@with_all_phases
@never_bls
@spec_state_test
def test_finality_rule_2(spec, state):
    # get past first two epochs that finality does not run on
    next_epoch(spec, state)
    apply_empty_block(spec, state)
    next_epoch(spec, state)
    apply_empty_block(spec, state)

    yield 'pre', state

    blocks = []
    for epoch in range(3):
        if epoch == 0:
            prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, True, False)
            check_finality(spec, state, prev_state, True, False, False)
        elif epoch == 1:
            prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, False, False)
            check_finality(spec, state, prev_state, False, True, False)
        elif epoch == 2:
            prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, False, True)
            # finalized by rule 2
            check_finality(spec, state, prev_state, True, False, True)
            assert state.finalized_checkpoint == prev_state.previous_justified_checkpoint

        blocks += new_blocks

    yield 'blocks', blocks
    yield 'post', state


@with_all_phases
@never_bls
@spec_state_test
def test_finality_rule_3(spec, state):
    """
    Test scenario described here
    https://github.com/ethereum/eth2.0-specs/issues/611#issuecomment-463612892
    """
    # get past first two epochs that finality does not run on
    next_epoch(spec, state)
    apply_empty_block(spec, state)
    next_epoch(spec, state)
    apply_empty_block(spec, state)

    yield 'pre', state

    blocks = []
    prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, True, False)
    blocks += new_blocks
    check_finality(spec, state, prev_state, True, False, False)

    # In epoch N, JE is set to N, prev JE is set to N-1
    prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, True, False)
    blocks += new_blocks
    check_finality(spec, state, prev_state, True, True, True)

    # In epoch N+1, JE is N, prev JE is N-1, and not enough messages get in to do anything
    prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, False, False)
    blocks += new_blocks
    check_finality(spec, state, prev_state, False, True, False)

    # In epoch N+2, JE is N, prev JE is N, and enough messages from the previous epoch get in to justify N+1.
    # N+1 now becomes the JE. Not enough messages from epoch N+2 itself get in to justify N+2
    prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, False, True)
    blocks += new_blocks
    # rule 2
    check_finality(spec, state, prev_state, True, False, True)

    # In epoch N+3, LJE is N+1, prev LJE is N, and enough messages get in to justify epochs N+2 and N+3.
    prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, True, True)
    blocks += new_blocks
    # rule 3
    check_finality(spec, state, prev_state, True, True, True)
    assert state.finalized_checkpoint == prev_state.current_justified_checkpoint

    yield 'blocks', blocks
    yield 'post', state