beer_song.rb

module Beer
  class Song
    VERSE_TEMPLATE = "%d bottles of beer on the wall, %d bottles of beer.\n" +
      "Take one down and pass it around, %d bottle%s of beer on the wall.\n"
    PENULTIMATE_VERSE = "1 bottle of beer on the wall, 1 bottle of beer.\n" +
      "Take it down and pass it around, no more bottles of beer on the wall.\n"
    FINAL_VERSE = "No more bottles of beer on the wall, no more bottles of beer.\n" +
      "Go to the store and buy some more, 99 bottles of beer on the wall.\n"

    def verses(starting, ending=0)
      starting.downto(ending).map {|number| verse(number) }.join("\n") + "\n"
    end

    def verse(number)
      case number
      when 1
        PENULTIMATE_VERSE
      when 0
        FINAL_VERSE
      else
        VERSE_TEMPLATE%[number, number, number - 1, number == 2 ? '' : 's' ]
      end
    end
  end
end

beer_song_test.rb

gem 'minitest'
require 'minitest/autorun'
require './beer_song'

class BeerSongTest < Minitest::Test

  V8 =
    "8 bottles of beer on the wall, 8 bottles of beer.\n" +
    "Take one down and pass it around, 7 bottles of beer on the wall.\n"

  V7 =
    "7 bottles of beer on the wall, 7 bottles of beer.\n" +
    "Take one down and pass it around, 6 bottles of beer on the wall.\n"

  V6 =
    "6 bottles of beer on the wall, 6 bottles of beer.\n" +
    "Take one down and pass it around, 5 bottles of beer on the wall.\n"

  V3 =
    "3 bottles of beer on the wall, 3 bottles of beer.\n" +
    "Take one down and pass it around, 2 bottles of beer on the wall.\n"

  V2 =
    "2 bottles of beer on the wall, 2 bottles of beer.\n" +
    "Take one down and pass it around, 1 bottle of beer on the wall.\n"

  V1 =
    "1 bottle of beer on the wall, 1 bottle of beer.\n" +
    "Take it down and pass it around, no more bottles of beer on the wall.\n"

  V0 =
    "No more bottles of beer on the wall, no more bottles of beer.\n" +
    "Go to the store and buy some more, 99 bottles of beer on the wall.\n"

  def combine_verses(*verses)
    verses.map { |v| "#{v}\n" }.join
  end

  def beer_song
    @beer_song = Beer::Song.new
  end

  def teardown
    @beer_song = nil
  end

  # Tests ...

  def test_a_typical_verse
    assert_equal V8, beer_song.verse(8)
  end

  def test_another_typical_verse
    assert_equal V3, beer_song.verse(3)
  end

  def test_verse_1
    assert_equal V1, beer_song.verse(1)
  end

  def test_verse_2
    assert_equal V2, beer_song.verse(2)
  end

  def test_verse_0
    assert_equal V0, beer_song.verse(0)
  end

  def test_several_verses
    expected = combine_verses(V8, V7, V6)
    assert_equal expected, beer_song.verses(8, 6)
  end

  def test_all_the_rest_of_the_verses
    expected = combine_verses(V3, V2, V1, V0)
    assert_equal expected, beer_song.verses(3)
  end
end