Chapter12Spec.scala

import Chapter12._
import org.scalatest.{FlatSpec, Matchers}

class Chapter12Spec extends FlatSpec with Matchers {

  "values" should "yield a collection of function inputs and outputs in a given range" in {
    //when
    val result: Seq[(Int, Int)] = values(x => x * x, -5, 5)

    //then
    result shouldBe Seq((-5, 25), (-4, 16), (-3, 9), (-2, 4), (-1, 1), (0, 0),
      (1, 1), (2, 4), (3, 9), (4, 16), (5, 25))
  }

  "largestElement" should "return the largest element of an array with reduceLeft" in {
    //given
    val arr = Array(5, 6, 1, 0, -2, 3, -1)

    //when
    val result: Int = largestElement(arr)

    //then
    result shouldBe 6
  }

  "factorial" should "be implemented using to and reduceLeft" in {
    //when & then
    factorial(-1) shouldBe 1
    factorial(0) shouldBe 1
    factorial(1) shouldBe 1
    factorial(5) shouldBe 120
  }

  "factorial2" should "be implemented using to and foldLeft" in {
    //when & then
    factorial2(-1) shouldBe 1
    factorial2(0) shouldBe 1
    factorial2(1) shouldBe 1
    factorial2(5) shouldBe 120
  }

  "largest" should "return the largest value of a function within a given sequence of inputs" in {
    //when
    val result: Int = largest(x => 10 * x - x * x, 1 to 10)

    //then
    result shouldBe 25
  }

  "largestAt" should "return the input at which the output is largest" in {
    //when
    val result: Int = largestAt(x => 10 * x - x * x, 1 to 10)

    //then
    result shouldBe 5
  }

  "adjustToPair" should "return the function that operates on a pair" in {
    //when & then
    adjustToPair(_ * _)((6, 7)) shouldBe 42
  }

  "mapPairs" should "compute the sums of the elements in pairs" in {
    //given
    val pairs = (1 to 10) zip (11 to 20)

    //when
    val result: Seq[Int] = mapPairs(pairs, _ + _)

    result shouldBe Seq(12, 14, 16, 18, 20, 22, 24, 26, 28, 30)
  }

  "correspondsLen" should "check that strings have the lengths from integers array" in {
    //when & then
    correspondsLen(Array(""), Array(0)) shouldBe true
    correspondsLen(Array(""), Array(1)) shouldBe false
    correspondsLen(Array("a"), Array(1)) shouldBe true
    correspondsLen(Array("a"), Array(2)) shouldBe false
    correspondsLen(Array("a", "bb", "ccc"), Array(1, 2, 3)) shouldBe true
    correspondsLen(Array("a", "bb", "ccc"), Array(1, 2, 3, 4)) shouldBe false
    correspondsLen(Array("a", "bb", "ccc"), Array(1, 2)) shouldBe false
  }

  "corresponds2" should "be implemented without currying" in {
    corresponds2(Array("a"), Array(1), (a: String, b: Int) => a.length == b) shouldBe true
  }

  "unless" should "work just like if, but with an inverted condition" in {
    //when & then
    var a = 0
    unless(a == 1) {
      a = 1
    }

    a shouldBe 1

    var b = 0
    unless(b == 0) {
      b = 1
    }

    b shouldBe 0
  }
}