info.gehrels.voting.singleTransferableVote.WeightedInclusiveGregoryMethodTest.java Source code

Introduction

Here is the source code for info.gehrels.voting.singleTransferableVote.WeightedInclusiveGregoryMethodTest.java

Source

/*
 * Copyright  2014 Benjamin Gehrels
 *
 * This file is part of The Single Transferable Vote Elections Library.
 *
 * The Single Transferable Vote Elections Web Interface 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.
 *
 * The Single Transferable Vote Elections Web Interface 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 The Single Transferable Vote
 * Elections Web Interface. If not, see <http://www.gnu.org/licenses/>.
 */
package info.gehrels.voting.singleTransferableVote;

import com.google.common.collect.ImmutableCollection;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import info.gehrels.voting.Ballot;
import info.gehrels.voting.Candidate;
import info.gehrels.voting.Election;
import org.apache.commons.math3.fraction.BigFraction;
import org.hamcrest.Matchers;
import org.junit.Test;

import static info.gehrels.voting.TestUtils.createBallot;
import static info.gehrels.voting.singleTransferableVote.VoteStateMatchers.aVoteState;
import static info.gehrels.voting.singleTransferableVote.VoteStateMatchers.withBallotId;
import static info.gehrels.voting.singleTransferableVote.VoteStateMatchers.withVoteWeight;
import static org.apache.commons.math3.fraction.BigFraction.ONE_HALF;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.hasItems;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;

public final class WeightedInclusiveGregoryMethodTest {
    private static final Candidate CANDIDATE_A = new Candidate("A");
    private static final Candidate CANDIDATE_B = new Candidate("B");
    private static final Candidate CANDIDATE_C = new Candidate("C");
    private static final Candidate CANDIDATE_D = new Candidate("D");

    private static final ImmutableSet<Candidate> CANDIDATES = ImmutableSet.of(CANDIDATE_A, CANDIDATE_B, CANDIDATE_C,
            CANDIDATE_D);
    private static final Election<Candidate> ELECTION = new Election<>("Example Office", CANDIDATES);
    private static final Ballot<Candidate> BALLOT_ABCD = createBallot("ABCD", ELECTION);
    private static final Ballot<Candidate> BALLOT_ACD = createBallot("ACD", ELECTION);
    private static final Ballot<Candidate> BALLOT_BCDA = createBallot("BCDA", ELECTION);
    private static final Ballot<Candidate> BALLOT_NO_VOTES = createBallot("", ELECTION);

    private static final ImmutableList<VoteState<Candidate>> VOTE_STATES_FIXTURE = ImmutableList.of(
            VoteState.forBallotAndElection(BALLOT_ABCD, ELECTION).get(),
            VoteState.forBallotAndElection(BALLOT_ACD, ELECTION).get().withVoteWeight(BigFraction.THREE_QUARTERS),
            VoteState.forBallotAndElection(BALLOT_BCDA, ELECTION).get(),
            VoteState.forBallotAndElection(BALLOT_NO_VOTES, ELECTION).get());

    private final STVElectionCalculationListener<Candidate> listenerMock = mock(
            STVElectionCalculationListener.class);
    private final WeightedInclusiveGregoryMethod<Candidate> wigm = new WeightedInclusiveGregoryMethod<>(
            listenerMock);

    private static final CandidateStates<Candidate> ALL_HOPEFUL_CANDIDATE_STATE = new CandidateStates<>(CANDIDATES);

    @Test
    public void reducesVoteWeightOfThoseBallotsThatHadTheElectedCandidateAsCurrentPreferredCandidate() {
        VoteWeightRecalculator<Candidate> voteWeightRecalculator = wigm.recalculatorFor();

        ImmutableCollection<VoteState<Candidate>> voteStates = voteWeightRecalculator.recalculateExceededVoteWeight(
                CANDIDATE_A, new BigFraction(7, 8), VOTE_STATES_FIXTURE, ALL_HOPEFUL_CANDIDATE_STATE);

        assertThat(voteStates,
                hasItems(
                        aVoteState(Matchers.<VoteState<Candidate>>allOf(withVoteWeight(ONE_HALF),
                                withBallotId(BALLOT_ABCD.id))),
                        aVoteState(Matchers.<VoteState<Candidate>>allOf(withBallotId(BALLOT_ACD.id),
                                withVoteWeight(new BigFraction(3, 8))))));
    }

    @Test
    public void reportsEachVoteWeightRedistribution() {
        VoteWeightRecalculator<Candidate> voteWeightRecalculator = wigm.recalculatorFor();

        voteWeightRecalculator.recalculateExceededVoteWeight(CANDIDATE_A, new BigFraction(7, 8),
                VOTE_STATES_FIXTURE, ALL_HOPEFUL_CANDIDATE_STATE);

        verify(listenerMock).redistributingExcessiveFractionOfVoteWeight(CANDIDATE_A, ONE_HALF);
    }

    @Test
    public void doesNotReduceVoteWeightOfThoseVotesThatDidNotHaveTheElectedCandidateAsCurrentPreferredCandidate() {
        VoteWeightRecalculator<Candidate> voteWeightRecalculator = wigm.recalculatorFor();

        ImmutableCollection<VoteState<Candidate>> voteStates = voteWeightRecalculator.recalculateExceededVoteWeight(
                CANDIDATE_A, BigFraction.ONE, VOTE_STATES_FIXTURE, ALL_HOPEFUL_CANDIDATE_STATE);

        assertThat(voteStates,
                hasItems(
                        aVoteState(Matchers.<VoteState<Candidate>>allOf(withBallotId(BALLOT_BCDA.id),
                                withVoteWeight(BigFraction.ONE))),
                        aVoteState(Matchers.<VoteState<Candidate>>allOf(withBallotId(BALLOT_NO_VOTES.id),
                                withVoteWeight(BigFraction.ONE)))));
    }

}