chapter_9d.rb

require 'minitest/reporters'
MiniTest::Unit.runner = MiniTest::SuiteRunner.new
MiniTest::Unit.runner.reporters << MiniTest::Reporters::SpecReporter.new
require 'minitest/autorun'

############## Page 215 ##############
class Gear
  # ...
  def gear_inches
    ratio * wheel.diameter
  end
end

############## Page 216 ##############
class Gear
  attr_reader :chainring, :cog, :wheel, :observer
  def initialize(args)
    # ...
    @observer  = args[:observer]
  end

  # ...

  def set_cog(new_cog)
    @cog = new_cog
    changed
  end

  def set_chainring(new_chainring)
    @chainring = new_chainring
    changed
  end

  def changed
    observer.changed(chainring, cog)
  end
# ...
end

############## Page ?? ##############
# Full listing for above
class Gear
  attr_reader :chainring, :cog, :wheel, :observer
  def initialize(args)
    @chainring = args[:chainring]
    @cog       = args[:cog]
    @wheel     = args[:wheel]
    @observer  = args[:observer]
  end

  def gear_inches
    ratio * wheel.diameter
  end

  def ratio
    chainring / cog.to_f
  end

  def set_cog(new_cog)
    @cog = new_cog
    changed
  end

  def set_chainring(new_chainring)
    @chainring = new_chainring
    changed
  end

  def changed
    observer.changed(chainring, cog)
  end

end

############## Page 217 ##############
class GearTest < MiniTest::Unit::TestCase

  def setup
    @observer = MiniTest::Mock.new
    @gear     = Gear.new(
                  chainring: 52,
                  cog:       11,
                  observer:  @observer)
  end

  def test_notifies_observers_when_cogs_change
    @observer.expect(:changed, true, [52, 27])
    @gear.set_cog(27)
    @observer.verify
  end

  def test_notifies_observers_when_chainrings_change
    @observer.expect(:changed, true, [42, 11])
    @gear.set_chainring(42)
    @observer.verify
  end
end