Add Meek STV test case

tests/data/meekm.blt

@@ -0,0 +1,14 @@
+4 2
+-2
+3 1 3 4 0
+4 1 3 2 0
+2 4 1 3 0
+1 2 0
+2 2 4 3 1 0
+1 3 4 2 0
+0
+"Adam"
+"Basil"
+"Charlotte"
+"Donald"
+"Title"

tests/test_meekm.py

@@ -0,0 +1,98 @@
+#   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.Fixed)
+	pyRCV2.numbers.set_dps(9)
+	
+	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withdrawn == [cand_b]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WITHDRAWN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