TennisGame.java

public interface TennisGame {
    void wonPoint(String playerName);
    String getScore();
}

TennisGame1.java

public class TennisGame1 implements TennisGame {

    private static final int LOVE = 0;
    private static final int FIFTEEN = 1;
    private static final int THIRTY = 2;
    private static final int FORTY = 3;
    private static final int OVER_FORTY = 4;

    private static String nameFor(int score) {
        if (score==FIFTEEN) {
            return Point.Fifteen.name(); 
        }
        
        return Point.Love.name();
    }

    private static enum Point {
        Love(LOVE), Fifteen(FIFTEEN), Thirty(THIRTY), Forty(FORTY), OverForty(OVER_FORTY);
        private final int score;

        private Point(int score) {
            this.score = score;
        }
        
        public Point fromScore(int score) {
            return null;
        }
        
        
    }
    private int m_score1 = 0;
    private int m_score2 = 0;
    private String player1Name;
    private String player2Name;

    public TennisGame1(String player1Name, String player2Name) {
        this.player1Name = player1Name;
        this.player2Name = player2Name;
    }

    public void wonPoint(String playerName) {
        if (playerName == "player1") {
            m_score1 += 1;
        } else {
            m_score2 += 1;
        }
    }

    public String getScore() {

        if (tie()) {
            return scoreForTie();
        } else if (possibleWin()) {
            return scoreForPossibleWin();
        }
        return scoreForNoTieAndNoWin();
    }

    private String scoreForNoTieAndNoWin() {
        String score = "";
        int tempScore;
        for (int i = 1; i < 3; i++) {
            if (i == 1) {
                tempScore = m_score1;
            } else {
                score += "-";
                tempScore = m_score2;
            }
            switch (tempScore) {
                case LOVE:
                    score += nameFor(tempScore);
                    break;
                case FIFTEEN:
                    score += nameFor(tempScore);
                    break;
                case THIRTY:
                    score += "Thirty";
                    break;
                case FORTY:
                    score += "Forty";
                    break;
            }
        }
        return score;
    }

    private String scoreForPossibleWin() {
        String score;
        int minusResult = m_score1 - m_score2;
        if (minusResult == 1) {
            score = "Advantage player1";
        } else if (minusResult == -1) {
            score = "Advantage player2";
        } else if (minusResult >= 2) {
            score = "Win for player1";
        } else {
            score = "Win for player2";
        }
        return score;
    }

    private String scoreForTie() {
        switch (m_score1) {
            case LOVE:
                return "Love-All";
            case FIFTEEN:
                return "Fifteen-All";
            case THIRTY:
                return "Thirty-All";
            case FORTY:
                return "Forty-All";
            default:
                return "Deuce";
        }
    }

    private boolean tie() {
        return m_score1 == m_score2;
    }

    private boolean possibleWin() {
        return m_score1 >= OVER_FORTY || m_score2 >= OVER_FORTY;
    }
}

TennisTest.java

import static org.junit.Assert.*;

import java.util.Arrays;
import java.util.Collection;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;
import org.junit.runners.Parameterized.Parameters;

@RunWith(Parameterized.class)
public class TennisTest {

    private int player1Score;
    private int player2Score;
    private String expectedScore;

    public TennisTest(int player1Score, int player2Score, String expectedScore) {
        this.player1Score = player1Score;
        this.player2Score = player2Score;
        this.expectedScore = expectedScore;
    }
    
    @Parameters
    public static Collection<Object[]> getAllScores() {
        return Arrays.asList(new Object[][] {
                { 0, 0, "Love-All" },
                { 1, 1, "Fifteen-All" },
                { 2, 2, "Thirty-All"},
                { 3, 3, "Forty-All"},
                { 4, 4, "Deuce"},
                
                { 1, 0, "Fifteen-Love"},
                { 0, 1, "Love-Fifteen"},
                { 2, 0, "Thirty-Love"},
                { 0, 2, "Love-Thirty"},
                { 3, 0, "Forty-Love"},
                { 0, 3, "Love-Forty"},
                { 4, 0, "Win for player1"},
                { 0, 4, "Win for player2"},
                
                { 2, 1, "Thirty-Fifteen"},
                { 1, 2, "Fifteen-Thirty"},
                { 3, 1, "Forty-Fifteen"},
                { 1, 3, "Fifteen-Forty"},
                { 4, 1, "Win for player1"},
                { 1, 4, "Win for player2"},

                { 3, 2, "Forty-Thirty"},
                { 2, 3, "Thirty-Forty"},
                { 4, 2, "Win for player1"},
                { 2, 4, "Win for player2"},
                
                { 4, 3, "Advantage player1"},
                { 3, 4, "Advantage player2"},
                { 5, 4, "Advantage player1"},
                { 4, 5, "Advantage player2"},
                { 15, 14, "Advantage player1"},
                { 14, 15, "Advantage player2"},

                { 6, 4, "Win for player1"},
                { 4, 6, "Win for player2"},
                { 16, 14, "Win for player1"},
                { 14, 16, "Win for player2"},
        });
    }

    public void checkAllScores(TennisGame game) {
        int highestScore = Math.max(this.player1Score, this.player2Score);
        for (int i = 0; i < highestScore; i++) {
            if (i < this.player1Score)
                game.wonPoint("player1");
            if (i < this.player2Score)
                game.wonPoint("player2");
        }
        assertEquals(this.expectedScore, game.getScore());
    }

    @Test
    public void checkAllScoresTennisGame1() {
        TennisGame1 game = new TennisGame1("player1", "player2");
        checkAllScores(game);
    }

    @Test
    public void checkAllScoresTennisGame2() {
        TennisGame2 game = new TennisGame2("player1", "player2");
        checkAllScores(game);
    }

    @Test
    public void checkAllScoresTennisGame3() {
        TennisGame3 game = new TennisGame3("player1", "player2");
        checkAllScores(game);
    }

}