Ruby Erreur de Nom - Uninitialized constant

Je suis en train de faire exercices et je suis
obtenir NameError:Unitialized Constant MyUnitTests::Room lors de l'exécution de test_ex47.rb.

test_ex47.rb:

require 'test/unit'
require_relative '../lib/ex47'

class MyUnitTests < Test::Unit::TestCase
    def test_room()
        gold = Room.new("Gold Room", """This room has gold in it you can grab. There's a doo to the north.""")
    assert_equal(gold.name, "GoldRoom")
    assert_equal(gold.paths, {})
end

def test_room_paths()
    center = Room.new("Center", "Test room in the center.")
    north = Room.new("North", "Test room in the north.")
    south = Room.new("South", "Test room in the south.")

    center.add_paths({:north => north, :south => south})
    assert_equal(center.go(:north), north)
    assert_equal(center.go(:south), south)
end

def test_map()
    start = Room.new("Start", "You can go west and down a hole.")
    west = Room.new("Trees", "There are trees here, you can go east.")
    down = Room.new("Dungeon", "It's dark down here, you can go up.")

    start.add_paths({:west => west, :down => down})
    west.add_paths({:east => start})
    down.add_paths({:up => start})

    assert_equal(start.go(:west), west)
    assert_equal(start.go(:west).go(:east), start)
    assert_equal(start.go(down).go(up), start)
end

end

ex47.rb est situé dans le dossier lib et ressemble:

class Room
aatr_accessor :name, :description, :paths

def initialize(name, description)
    @name = name
    @description = description
    @paths = {}
end

def go(direction)
    @paths[direction]
end

def add_paths(paths)
    @paths.update(paths)
end
end

Erreur:

Finished tests in 0.000872s, 3440.3670 tests/s, 0.0000 assertions/s.

  1) Error:
test_map(MyUnitTests):
NameError: uninitialized constant MyUnitTests::Room
    test_ex47.rb:22:in `test_map'

  2) Error:
test_room(MyUnitTests):
NameError: uninitialized constant MyUnitTests::Room
    test_ex47.rb:6:in `test_room'

  3) Error:
test_room_paths(MyUnitTests):
NameError: uninitialized constant MyUnitTests::Room
    test_ex47.rb:12:in `test_room_paths'

3 tests, 0 assertions, 0 failures, 3 errors, 0 skips]