La solution que j'avais réalisée avant

BowlingTest.java

package test;

import static org.junit.Assert.*;

import main.Game;

import org.junit.Before;
import org.junit.Test;

public class BowlingTest {
	
	private Game _game;

	@Before
	public void before() {
		_game = new Game();
	}

	@Test
	public void a_gutter_game_should_score_0() {
		rollMany(_game, 20, 0);
		assertEquals(0, _game.score());
	}
	
	@Test
	public void a_game_with_one_ninepin_down_should_score_1() {
		_game.roll(1);
		rollMany(_game, 19, 0);
		assertEquals(1, _game.score());
	}
	
	@Test
	public void a_spare_should_double_the_next_roll() {
		_game.roll(5);
		_game.roll(5);
		_game.roll(4);
		rollMany(_game, 17, 0);
		
		assertEquals(18, _game.score());
	}

	@Test
	public void a_strike_should_double_the_2_next_rolls() {
		_game.roll(10);
		_game.roll(2);
		_game.roll(3);
		rollMany(_game, 16, 0);
		
		assertEquals(20, _game.score());
	}
	@Test
	public void a_strike_is_not_a_spare() {
		_game.roll(10);
		_game.roll(0);
		_game.roll(4);
		rollMany(_game, 16, 0);
		
		assertEquals(18, _game.score());
	}
	@Test
	public void a_spare_should_not_span_multiple_frames() {
		_game.roll(0);
		_game.roll(5);
		_game.roll(5);
		_game.roll(2);
		rollMany(_game, 16, 0);
		
		assertEquals(12, _game.score());
	}
	
	@Test
	public void a_game_with_only_ones_should_score_20() {
		rollMany(_game, 20, 1);

		assertEquals(20, _game.score());
	}
	
	@Test
	public void a_second_roll_10_should_not_be_a_strike() {
		_game.roll(0);
		_game.roll(10);
		_game.roll(5);
		_game.roll(2);
		rollMany(_game, 16, 0);
		
		assertEquals(22, _game.score());
	}
	@Test
	public void a_perfect_game_should_score_300()
	{
		rollMany(_game, 12, 10);
		
		assertEquals(300, _game.score());
	}
	
	private void rollMany(Game game, int count, int score) {
		for(int i = 0; i < count; i++) {
			game.roll(score);
		}
	}
}

Game.java

package main;

import java.util.ArrayList;

public class Game {

	private ArrayList<Integer> _rolls = new ArrayList<Integer>();
	
	public void roll(int score) {
		_rolls.add(score);
	}

	public int score() {
		int score = 0;
		int frameIndex = 0;
		for(int frame = 0; frame < 10; frame++) {

			if (isStrike(frameIndex)) {
				score += 10 + strikeBonus(frameIndex);
				frameIndex++;
			}
			else if (isSpare(frameIndex)) {
				score += 10 + spareBonus(frameIndex);
				frameIndex += 2;
			}
			else {
				score += frameScore(frameIndex);
				frameIndex += 2;
			}
		}
		return score;
	}

	private boolean isStrike(int frameIndex) {
		return _rolls.get(frameIndex) == 10;
	}

	private boolean isSpare(int frameIndex) {
		return _rolls.get(frameIndex) + _rolls.get(frameIndex+1) == 10;
	}
	
	private int strikeBonus(int frameIndex) {
		return _rolls.get(frameIndex+1) + _rolls.get(frameIndex+2);
	}
	private int spareBonus(int frameIndex) {
		return _rolls.get(frameIndex+2);
	}
	
	private int frameScore(int frameIndex) {
		return _rolls.get(frameIndex) + _rolls.get(frameIndex+1);
	}
}