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pyRCV2/tests/test_meekm.py

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2021-01-14 00:47:44 +11:00
# pyRCV2: Preferential vote counting
# Copyright © 2020–2021 Lee Yingtong Li (RunasSudo)
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
import pytest
import pyRCV2.blt
import pyRCV2.numbers
from pyRCV2.method.base_stv import STVException
from pyRCV2.method.meek import MeekSTVCounter
from pyRCV2.model import CandidateState, CountCompleted
from pyRCV2.ties import TiesBackwards
def test_meekm():
"""Compare count of meekm.blt with model result produced by Hill et al. reference implementation"""
pyRCV2.numbers.set_numclass(pyRCV2.numbers.FixedGuarded)
pyRCV2.numbers.set_dps(4)
2021-01-14 00:47:44 +11:00
with open('tests/data/meekm.blt', 'r') as f:
election = pyRCV2.blt.readBLT(f.read())
assert len(election.candidates) == 4
cand_a = next(c for c in election.candidates if c.name == 'Adam')
cand_b = next(c for c in election.candidates if c.name == 'Basil')
cand_c = next(c for c in election.candidates if c.name == 'Charlotte')
cand_d = next(c for c in election.candidates if c.name == 'Donald')
assert election.withdrawn == [cand_b]
counter = MeekSTVCounter(election, {
'quota': 'droop_exact',
'quota_criterion': 'gt',
'quota_mode': 'progressive',
'ties': []
})
# Stage 1
result = counter.reset()
assert result.comment == 'First preferences'
assert result.total == pyRCV2.numbers.Num('13')
assert result.quota == pyRCV2.numbers.Num('4')
assert len(result.candidates.impl) == 4
assert result.candidates[cand_a].state == CandidateState.ELECTED
assert result.candidates[cand_b].state == CandidateState.WITHDRAWN
assert result.candidates[cand_c].state == CandidateState.HOPEFUL
assert result.candidates[cand_d].state == CandidateState.HOPEFUL
assert result.candidates[cand_a].votes == pyRCV2.numbers.Num('7')
assert result.candidates[cand_c].votes == pyRCV2.numbers.Num('1')
assert result.candidates[cand_d].votes == pyRCV2.numbers.Num('4')
assert result.exhausted.votes == pyRCV2.numbers.Num('1')
# Stage 2
result = counter.step()
assert result.total == pyRCV2.numbers.Num('13')
assert result.quota == pyRCV2.numbers.Num('4')
assert result.candidates[cand_a].state == CandidateState.ELECTED
assert result.candidates[cand_b].state == CandidateState.WITHDRAWN
assert result.candidates[cand_c].state == CandidateState.HOPEFUL
assert result.candidates[cand_d].state == CandidateState.HOPEFUL
assert result.candidates[cand_a].votes == pyRCV2.numbers.Num('4')
assert result.candidates[cand_c].votes == pyRCV2.numbers.Num('4')
assert result.candidates[cand_d].votes == pyRCV2.numbers.Num('4')
assert result.exhausted.votes == pyRCV2.numbers.Num('1')
# Stage 3
# FIXME: This fails in Javascript (rounding errors?)
with pytest.raises(STVException) as exc_info:
result = counter.step()
assert exc_info.value.message == 'Unable to resolve tie'
# Retry further stages
counter.options['ties'] = [TiesBackwards(counter)]
result = counter.step()
while not isinstance(result, CountCompleted):
result = counter.step()
assert result.candidates[cand_a].state == CandidateState.ELECTED
assert result.candidates[cand_b].state == CandidateState.WITHDRAWN
assert result.candidates[cand_c].state == CandidateState.EXCLUDED # Charlotte loses the tie if broken backwards
assert result.candidates[cand_d].state == CandidateState.ELECTED