CodeIQに出題した「カラオケマシン問題」の解答テンプレートです。詳しくはこちら: http://blog.jnito.com/entry/2014/06/06/104420

karaoke_machine.rb

# coding: utf-8

class KaraokeMachine
  def initialize(melody)
  end

  def transpose(amount)
    "" # これは仮実装なので消してください
  end
end

describe KaraokeMachine do
  it "メロディ無し" do
    melody = ""
    answer = melody
    expect(KaraokeMachine.new(melody).transpose(0)).to eq answer
  end

  # ここから下のコメントを外していって、テストを全部パスさせてください！

  # it "変更無し" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = melody
  #   expect(KaraokeMachine.new(melody).transpose(0)).to eq answer
  # end
  #
  # it "2上げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = "D E F# G |F# E D   |F# G A B |A G F#   |D   D   |D   D   |DDEEF#F#GG|F# E D   "
  #   expect(KaraokeMachine.new(melody).transpose(2)).to eq answer
  # end
  #
  # it "7上げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = "G A B C |B A G   |B C D E |D C B   |G   G   |G   G   |GGAABBCC|B A G   "
  #   expect(KaraokeMachine.new(melody).transpose(7)).to eq answer
  # end
  #
  # it "1下げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = "B C# D# E |D# C# B   |D# E F# G# |F# E D#   |B   B   |B   B   |BBC#C#D#D#EE|D# C# B   "
  #   expect(KaraokeMachine.new(melody).transpose(-1)).to eq answer
  # end
  #
  # it "7下げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = "F G A A# |A G F   |A A# C D |C A# A   |F   F   |F   F   |FFGGAAA#A#|A G F   "
  #   expect(KaraokeMachine.new(melody).transpose(-7)).to eq answer
  # end
  #
  # it "1オクターブ上げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = melody
  #   expect(KaraokeMachine.new(melody).transpose(12)).to eq answer
  # end
  #
  # it "1オクターブ下げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = melody
  #   expect(KaraokeMachine.new(melody).transpose(-12)).to eq answer
  # end
  #
  # it "14上げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = "D E F# G |F# E D   |F# G A B |A G F#   |D   D   |D   D   |DDEEF#F#GG|F# E D   "
  #   expect(KaraokeMachine.new(melody).transpose(14)).to eq answer
  # end
  #
  # it "13下げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = "B C# D# E |D# C# B   |D# E F# G# |F# E D#   |B   B   |B   B   |BBC#C#D#D#EE|D# C# B   "
  #   expect(KaraokeMachine.new(melody).transpose(-13)).to eq answer
  # end
  #
  # it "2オクターブ上げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = melody
  #   expect(KaraokeMachine.new(melody).transpose(24)).to eq answer
  # end
  #
  # it "2オクターブ下げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = melody
  #   expect(KaraokeMachine.new(melody).transpose(-24)).to eq answer
  # end
  #
  # it "26上げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = "D E F# G |F# E D   |F# G A B |A G F#   |D   D   |D   D   |DDEEF#F#GG|F# E D   "
  #   expect(KaraokeMachine.new(melody).transpose(26)).to eq answer
  # end
  #
  # it "25上げる" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   answer = "B C# D# E |D# C# B   |D# E F# G# |F# E D#   |B   B   |B   B   |BBC#C#D#D#EE|D# C# B   "
  #   expect(KaraokeMachine.new(melody).transpose(-25)).to eq answer
  # end
  #
  # it "6上げる(メロディはF#から開始)" do
  #   melody = "F# G# A# B |A# G# F#   |A# B C# D# |C# B A#   |F#   F#   |F#   F#   |F#F#G#G#A#A#BB|A# G# F#   "
  #   answer = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   expect(KaraokeMachine.new(melody).transpose(6)).to eq answer
  # end
  #
  # it "6下げる(メロディはF#から開始)" do
  #   melody = "F# G# A# B |A# G# F#   |A# B C# D# |C# B A#   |F#   F#   |F#   F#   |F#F#G#G#A#A#BB|A# G# F#   "
  #   answer = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   expect(KaraokeMachine.new(melody).transpose(-6)).to eq answer
  # end
  #
  # it "連続してtransposeを呼び出す" do
  #   melody = "C D E F |E D C   |E F G A |G F E   |C   C   |C   C   |CCDDEEFF|E D C   "
  #   karaoke = KaraokeMachine.new(melody)
  #
  #   answer = melody
  #   expect(karaoke.transpose(0)).to eq answer
  #
  #   answer = "D E F# G |F# E D   |F# G A B |A G F#   |D   D   |D   D   |DDEEF#F#GG|F# E D   "
  #   expect(karaoke.transpose(2)).to eq answer
  #
  #   answer = "B C# D# E |D# C# B   |D# E F# G# |F# E D#   |B   B   |B   B   |BBC#C#D#D#EE|D# C# B   "
  #   expect(karaoke.transpose(-1)).to eq answer
  # end
end

公開ありがとうございます！
ぜひ挑戦したいと思っていたので解いてみました。

7年前のものにコメントするのもどうかとは思いますが、93行目は"25下げる"ですね。