Scala coding dojo 20/06/2013 - Code Kata - Prime Factors Calculator http://craftsmanship.sv.cmu.edu/exercises/prime-factors-kata

PrimeFactorCalculator.scala

import java.util
import scala.collection.mutable.ListBuffer

object PrimeFactorCalculator {
  def prime(number: Integer):Boolean = {
    if (number < 2) return false
    if (number == 2) return true
    for (i <- 3 to Math.sqrt(number.toDouble).toInt by 2 if (number % i == 0))
       return false
    true
  }

  def primeFactors(number: Integer):List[Int] = {
    val factors:ListBuffer[Int] = new ListBuffer[Int]()
    for (i <- 2 to number)
      if (number % i == 0 && prime(i)) {
        factors += i
      }
    println(factors)
    factors.toList
  }
}

PrimeFactorCalculatorTest.scala

import org.scalatest.FunSpec

class PrimeFactorCalculatorTest extends FunSpec {

  describe("Prime factor PrimeFactorCalculator") {
    it("should identify prime numbers") {
      assert(!PrimeFactorCalculator.prime(0))
      assert(PrimeFactorCalculator.prime(3))
      assert(!PrimeFactorCalculator.prime(35))
      assert(PrimeFactorCalculator.prime(2))
      assert(PrimeFactorCalculator.prime(17))
      assert(!PrimeFactorCalculator.prime(1))
      assert(!PrimeFactorCalculator.prime(-11))
    }
    it("should output a list of prime factors for a number") {
      assert(PrimeFactorCalculator.primeFactors(15) == List(3, 5))
      assert(PrimeFactorCalculator.primeFactors(17) == List(17))
      assert(PrimeFactorCalculator.primeFactors(0) == List())
      assert(PrimeFactorCalculator.primeFactors(1) == List())
      assert(PrimeFactorCalculator.primeFactors(-1) == List())
    }
  }
}