Bowling Game Kata - Scala implementation http://butunclebob.com/ArticleS.UncleBob.TheBowlingGameKata

BowlingGame.scala

class BowlingGame {
  var moves = Vector.empty[Int]

  def roll(i: Int) = {
    moves = moves :+ i
  }

  def score: Int = score()

  def score(i: Int = 0, acc: Int = 0, frames: Int = 0): Int =
    if (i >= moves.size || frames == 10) acc else {
      val first = moves(i)
      if (first == 10) score(i + 1, acc + 10 + moves(i + 1) + moves(i + 2), frames + 1)
      else {
        val second = moves(i + 1)
        if (first + second == 10) score(i + 2, acc + 10 + moves(i + 2), frames + 1)
        else score(i + 2, acc + first + second, frames + 1)
      }
    }

}

BowlingTest.scala

import org.junit.Test

class BowlingTest {

  @Test
  def scoreShouldBeZero =
    testAllBalls(0, 0)

  @Test
  def scoreShouldBe20 =
    testAllBalls(1, 20)

  @Test
  def scoreAfterOneSpare = {
    val game = new BowlingGame
    rollSpare(game)
    repeatRoll(18, 1, game)
    assert(game.score == 29, game.score)
  }

  def repeatRoll(count: Int, ball: Int, game: BowlingGame) =
    for (i <- 1 to count) game.roll(ball)

  @Test
  def scoreAfterOneSpareInSecondFrame = {
    val game = new BowlingGame
    repeatRoll(2, 0, game)
    rollSpare(game)
    repeatRoll(16, 1, game)
    assert(game.score == 27, game.score)
  }

  @Test
  def scoreAfterOneStrikeInSecondFrame = {
    val game = new BowlingGame
    repeatRoll(2, 0, game)
    game.roll(10)
    repeatRoll(16, 4, game)
    assert(game.score == 10 + 8 + 8 + 14 * 4, game.score)
  }

  @Test
  def scoreForRealGame = {
    val game = new BowlingGame
    for (i <- Seq(1, 4, 4, 5, 6, 4, 5, 5, 10, 0, 1, 7, 3, 6, 4, 10, 2, 8, 6)) game.roll(i)
    assert(game.score == 133, game.score)

  }

  @Test
  def scoreAfterAllStrike = {
    val game = new BowlingGame
    repeatRoll(12, 10, game)
    assert(game.score == 300, game.score)
  }

  def rollSpare(game: BowlingGame) = {
    game.roll(5)
    game.roll(5)
  }

  def testAllBalls(ball: Int, expected: Int) = {
    val game = new BowlingGame
    for (i <- 1 to 20) game.roll(ball)
    assert(game.score == expected, game.score)

  }
}