From: Dark Ambient <sambient@...>
Date: 2006-07-05T20:33:27+09:00
Subject: Pickaxe code error

Not sure what's going on with some code in Programming Ruby, it's
early on where a SongList container is being created and test units
are run.
I'm receiving this error:

  1) Error:
test_delete(TestSongList):
NameError: uninitialized constant TestSongList::Song
    pickaxe_SongListContainer.rb:52:in `test_delete'

the rb:52 won't be right as I've put notes in comments between the
code, which I'm stripping here.  Perhaps someone is familiar with
example.  I checked errata with no luck..TIA

require 'test/unit'

class SongList
  def initialize
    @songs = Array.new
  end

  def append(song)
    #songs.push(song)
    self
  end

  def delete_first
    @songs.shift
  end

  def delete_last
    @songs.pop
  end

  def [](index)
    @songs[index]
  end
end


class TestSongList < Test::Unit::TestCase
  def test_delete
    list = SongList.new
    s1 = Song.new('title1', 'artist1', 1)
    s2 = Song.new('title2', 'artist2', 2)
    s3 = Song.new('title3', 'artist3', 3)
    s4 = Song.new('title4', 'artist4', 4)

    list.append(s1).append(s2).append(s3).append(s4)

    assert_equal(s1, list[0])
    assert_equal(s3, list[2])
    assert_nil(list[9])

    assert_equal(s1,  list.delete_first)
    assert_equal(s2,  list.delete_first)
    assert_equal(s4,  list.delete_last)
    assert_equal(s3,  list.delete_last)
    assert_nil(list.delete_last)
  end
end