haskell-homework/test/Homework/Ch01/HanoiSpec.hs

module Homework.Ch01.HanoiSpec where

import Homework.Ch01.Hanoi
import Test.Hspec

spec :: Spec
spec = describe "Hanoi" $ do
  -- Testing the solver function
  describe "hanoi" $ do
    -- helper to construct a hanoi function with preconfigured labels
    let hanoiOf = hanoi "a" "b" "c"

    it "can solve for a stack of 1 disc" $ do
      hanoiOf 1 --          a@[1] b@[] c@[]
        `shouldBe` Right
          [ Move "a" "c" -- a@[]  b@[] c@[1]
          ]

    it "can solve for a stack of 2 discs" $ do
      hanoiOf 2 --           a@[2, 1] b@[]  c@[]
        `shouldBe` Right
          [ Move "a" "c", -- a@[2]    b@[]  c@[1]
            Move "a" "b", -- a@[]     b@[2] c@[1]
            Move "c" "a", -- a@[1]    b@[2] c@[]
            Move "a" "c", -- a@[1]    b@[]  c@[2]
            Move "a" "c" --  a@[]     b@[]  c@[2, 1]
          ]

    it "can solve for a stack of 3 discs" $ do
      hanoiOf 3 --           a@[3, 2, 1] b@[]     c@[]
        `shouldBe` Right
          [ Move "a" "c", -- a@[3, 2]    b@[]     c@[1]
            Move "a" "b", -- a@[3]       b@[2]    c@[1]
            Move "c" "b", -- a@[3]       b@[2, 1] c@[]
            Move "a" "c", -- a@[]        b@[2, 1] c@[3]
            Move "b" "a", -- a@[1]       b@[2]    c@[3]
            Move "b" "c", -- a@[1]       b@[]     c@[3, 2]
            Move "a" "c" --  a@[]        b@[]     c@[3, 2, 1]
          ]

  -- Testing individual moves
  describe "move" $ do
    it "moves the smallest peg from peg A to peg C if peg C's disc is bigger" $ do
      let emptyPegs = initPegs "a" "b" "c" 0
          pegs =
            emptyPegs
              { pegsPegA = (emptyPeg "a") {pegDiscs = [Disc 3, Disc 1]},
                pegsPegC = (emptyPeg "c") {pegDiscs = [Disc 2]}
              }
          -- run the function
          (moveMade, pegsAfterMove) = move pegs

      -- a move should have been made
      moveMade `shouldBe` Just (Move "a" "c")
      -- the pegs should have changed
      pegsAfterMove
        `shouldBe` pegs
          { pegsPegA = (pegsPegA pegs) {pegDiscs = [Disc 3]},
            pegsPegC = (pegsPegC pegs) {pegDiscs = [Disc 2, Disc 1]}
          }

  -- Testing constructor for a set of pegs
  describe "initPegs" $ do
    it "creates pegs with labels and fills the first peg with discs" $ do
      initPegs "a" "b" "c" 3
        `shouldBe` Pegs
          { pegsPegA = Peg {pegLabel = "a", pegDiscs = [Disc 3, Disc 2, Disc 1]},
            pegsPegB = Peg {pegLabel = "b", pegDiscs = []},
            pegsPegC = Peg {pegLabel = "c", pegDiscs = []}
          }

  -- Testing constructor for a peg with discs
  describe "fillPeg" $ do
    it "creates a list of disks from biggest to smallest" $ do
      fillPeg "a" 3
        `shouldBe` Peg
          { pegLabel = "a",
            pegDiscs = [Disc 3, Disc 2, Disc 1]
          }

  -- Testing constructor for a peg without discs
  describe "emptyPeg" $ do
    it "creates an empty peg" $ do
      emptyPeg "a"
        `shouldBe` Peg
          { pegLabel = "a",
            pegDiscs = []
          }

  -- Testing constructor for a stack of discs
  describe "stackDiscs" $ do
    it "should create a stack of discs from largest to smallest" $ do
      stackDiscs 3 `shouldBe` [Disc 3, Disc 2, Disc 1]