I am trying to create an ex48.rb based on a TEST
This is an assignment from the following website:
http://ruby.learncodethehardway.org/book/ex48.html

HEre what I've done so far without success
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# ex48.rb
module Lexicon
 class Pair

   attr_accessor :token, :word
 # the token are: direction, verb, stop, noun, number
 # the words are the words from those tokens
   def initialize(token, word)
     @token = token
     @word =  word
   end


   def scan(stuff)
     @words = stuff.split()
     if @words.include? @word
       return token
     else
       puts "The word %s was not found" % @token
     end
   end

   def add_words(words)
     @words.update(words)
   end

   stuf = gets.comp()
end


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# /lib/lexicon.rb
Direction = ['north', 'south', 'east', 'west', 'down', 'up', 'left', 'right']
Verbs = ['go', 'stop', 'kill', 'eat']
Stop_words = ['the', 'in', 'of', 'from', 'at', 'it']
Nouns = ['door', 'bear', 'princess', 'cabinet']

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ERROR MESSAGE I'M GETTING BELLOW

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osiris:test Richardson$ ruby test_lexicon.rb
test_lexicon.rb:6:in `<class:LexiconTests>': uninitialized constant LexiconTests::Lexicon (NameError)
	from test_lexicon.rb:4:in `<main>'
osiris:test Richardson$

-----------

TEST file Below

------------

require 'test/unit'
require_relative "../lib/lexicon"

class LexiconTests < Test::Unit::TestCase

  Pair = Lexicon::Pair
  @@lexicon = Lexicon.new()

  def test_directions()
    assert_equal([Pair.new(:direction, 'north')], @@lexicon.scan("north"))
    result = @@lexicon.scan("north south east")
    assert_equal(result, [Pair.new(:direction, 'north'),
                 Pair.new(:direction, 'south'),
                 Pair.new(:direction, 'east')])
  end

  def test_verbs()
    assert_equal(@@lexicon.scan("go"), [Pair.new(:verb, 'go')])
    result = @@lexicon.scan("go kill eat")
    assert_equal(result, [Pair.new(:verb, 'go'),
                 Pair.new(:verb, 'kill'),
                 Pair.new(:verb, 'eat')])
  end

  def test_stops()
    assert_equal(@@lexicon.scan("the"), [Pair.new(:stop, 'the')])
    result = @@lexicon.scan("the in of")
    assert_equal(result, [Pair.new(:stop, 'the'),
                 Pair.new(:stop, 'in'),
                 Pair.new(:stop, 'of')])
  end

  def test_nouns()
    assert_equal(@@lexicon.scan("bear"), [Pair.new(:noun, 'bear')])
    result = @@lexicon.scan("bear princess")
    assert_equal(result, [Pair.new(:noun, 'bear'),
                 Pair.new(:noun, 'princess')])
  end

  def test_numbers()
    assert_equal(@@lexicon.scan("1234"), [Pair.new(:number, 1234)])
    result = @@lexicon.scan("3 91234")
    assert_equal(result, [Pair.new(:number, 3),
                 Pair.new(:number, 91234)])
  end

  def test_errors()
    assert_equal(@@lexicon.scan("ASDFADFASDF"), [Pair.new(:error, 'ASDFADFASDF')])
    result = @@lexicon.scan("bear IAS princess")
    assert_equal(result, [Pair.new(:noun, 'bear'),
                 Pair.new(:error, 'IAS'),
                 Pair.new(:noun, 'princess')])
  end

end