Bowling Game

BowlingGameTest.java

package net.davidculpepper;

import org.junit.Test;

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.MatcherAssert.assertThat;

public class BowlingGameTest {

    Game sut = new Game();

    @Test
    public void gutter_test() {
        rollMany(20, 0);
        assertThat(sut.finalScore(), is(0));
    }

    @Test
    public void single_pin_test() {
        sut.roll(1);
        rollMany(19, 0);
        assertThat(sut.finalScore(), is(1));
    }

    @Test
    public void spare_test() {
        rollSpare();
        sut.roll(1);
        rollMany(17, 0);
        assertThat(sut.finalScore(), is(12));
    }

    @Test
    public void strike_test() {
        rollStrike();
        sut.roll(4);
        sut.roll(3);
        rollMany(16, 0);
        assertThat(sut.finalScore(), is(24));
    }

    @Test
    public void perfect_game_test() {
        rollMany(12, 10);
        assertThat(sut.finalScore(), is(300));
    }

    private void rollMany(int numRolls, int pins) {
        for (int i = 0; i < numRolls; i++) {
            sut.roll(pins);
        }
    }

    private void rollStrike() {
        sut.roll(10);
    }

    private void rollSpare() {
        sut.roll(6);
        sut.roll(4);
    }
}

Game.java

package net.davidculpepper;

import java.util.ArrayList;
import java.util.List;

public class Game {
    private List<Integer> rolls = new ArrayList<Integer>();

    public void roll(int numberOfPins) {
        rolls.add(numberOfPins);
    }

    public int finalScore() {
        int score = 0;
        int ball = 0;
        for (int frame = 0; frame < 10; frame++) {
            score += rolls.get(ball);
            score += rolls.get(ball + 1);

            if (isStrike(ball)) {
                score += rolls.get(ball + 2);
                ball++;
            } else if (isSpare(ball)) {
                score += rolls.get(ball + 2);
                ball += 2;
            } else {
                ball += 2;
            }
        }
        return score;
    }

    private boolean isStrike(int ball) {
        return rolls.get(ball) == 10;
    }

    private boolean isSpare(int ball) {
        return rolls.get(ball) + rolls.get(ball + 1) == 10;
    }
}