Scala spec unit tests

Question

I ve got the following class and I want to write some Spec test cases, but I am really new to it and I don't know how to start. My class do loke like this:

class Board{

  val array = Array.fill(7)(Array.fill(6)(None:Option[Coin]))

  def move(x:Int, coin:Coin) {
    val y = array(x).indexOf(None)
    require(y >= 0) 
    array(x)(y) = Some(coin)
   }

  def apply(x: Int, y: Int):Option[Coin] = 
     if (0 <= x && x < 7 && 0 <= y && y < 6) array(x)(y)
     else None

  def winner: Option[Coin] = winner(Cross).orElse(winner(Naught))

  private def winner(coin:Coin):Option[Coin] = {
    val rows = (0 until 6).map(y => (0 until 7).map( x => apply(x,y)))
    val cols = (0 until 7).map(x => (0 until 6).map( y => apply(x,y)))
    val dia1 = (0 until 4).map(x => (0 until 6).map( y => apply(x+y,y)))
    val dia2 = (3 until 7).map(x => (0 until 6).map( y => apply(x-y,y)))

    val slice = List.fill(4)(Some(coin))
    if((rows ++ cols ++ dia1 ++ dia2).exists(_.containsSlice(slice))) 
      Some(coin)
    else None
  }  

  override def toString = {
    val string = new StringBuilder
    for(y <- 5 to 0 by -1; x <- 0 to 6){
        string.append(apply(x, y).getOrElse("_"))
        if (x == 6) string.append ("\n") 
        else string.append("|")
    }
    string.append("0 1 2 3 4 5 6\n").toString
  }
}

Thank you!

Answer 1

I suggest you throw all that code out -- well, save it somewhere, but start from zero using TDD.

The Specs2 site has plenty examples of how to write tests, but use TDD -- test driven design -- to do it. Adding tests after the fact is suboptimal, to say the least.

So, think of the most simple case you want to handle of the most simple feature, write a test for that, see it fail, write the code to fix it. Refactor if necessary, and repeat for the next most simple case.

If you want help with how to do TDD in general, I heartily endorse the videos about TDD available on Clean Coders. At the very least, watch the second part where Bob Martin writes a whole class TDD-style, from design to end.

If you know how to do testing in general but are confused about Scala or Specs, please be much more specific about what your questions are.

Answer 2

I can only second Daniel's suggestion, because you'll end up with a more practical API by using TDD.

I also think that your application could be nicely tested with a mix of specs2 and ScalaCheck. Here the draft of a Specification to get you started:

  import org.specs2._
  import org.scalacheck.{Arbitrary, Gen}

  class TestSpec extends Specification with ScalaCheck { def is =

    "moving a coin in a column moves the coin to the nearest empty slot" ! e1^
    "a coin wins if"                                                     ^
      "a row contains 4 consecutive coins"                               ! e2^
      "a column contains 4 consecutive coins"                            ! e3^
      "a diagonal contains 4 consecutive coins"                          ! e4^
                                                                         end

    def e1 = check { (b: Board, x: Int, c: Coin) =>
      try { b.move(x, c) } catch { case e => () }
      // either there was a coin before somewhere in that column
      // or there is now after the move
      (0 until 6).exists(y => b(x, y).isDefined)
    }

    def e2 = pending
    def e3 = pending
    def e4 = pending

    /**
     * Random data for Coins, x position and Board
     */
    implicit def arbitraryCoin: Arbitrary[Coin]     = Arbitrary { Gen.oneOf(Cross,       Naught) }
    implicit def arbitraryXPosition: Arbitrary[Int] = Arbitrary { Gen.choose(0, 6) }
    implicit def arbitraryBoardMove: Arbitrary[(Int, Coin)]   = Arbitrary {
      for {
        coin <- arbitraryCoin.arbitrary
        x    <- arbitraryXPosition.arbitrary
      } yield (x, coin)
    }
    implicit def arbitraryBoard: Arbitrary[Board]   = Arbitrary {
      for {
        moves <- Gen.listOf1(arbitraryBoardMove.arbitrary)
      } yield {
        val board = new Board
        moves.foreach { case (x, coin) => 
          try { board.move(x, coin) } catch { case e => () }}
          board
      }
    }


  }

  object Cross extends Coin {
    override def toString = "x"
  }
  object Naught extends Coin {
    override def toString = "o"
  }
  sealed trait Coin

The e1 property I've implemented is not the real thing because it doesn't really check that we moved the coin to the nearest empty slot, which is what your code and your API suggests. You will also want to change the generated data so that the Boards are generated with an alternation of x and o. That should be a great way to learn how to use ScalaCheck!