chapter_9b.rb

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

############## Page ??? ##############
# The Wheel class expected by the following test
class Wheel
  attr_reader :rim, :tire
  def initialize(rim, tire)
    @rim       = rim
    @tire      = tire
  end

  def diameter
    rim + (tire * 2)
  end
# ...
end

############## Page 205 ##############
class Gear
  attr_reader :chainring, :cog, :wheel
  def initialize(args)
    @chainring = args[:chainring]
    @cog       = args[:cog]
    @wheel     = args[:wheel]
  end

  def gear_inches
      # The object in the 'wheel' variable
      #   plays the 'Diameterizable' role.
    ratio * wheel.diameter
  end

  def ratio
    chainring / cog.to_f
  end
# ...
end

############## Page 206 ##############
class GearTest < MiniTest::Unit::TestCase
  def test_calculates_gear_inches
    gear =  Gear.new(
              chainring: 52,
              cog:       11,
              wheel:     Wheel.new(26, 1.5))

    assert_in_delta(137.1,
                    gear.gear_inches,
                    0.01)
  end
end

############## Page 207 ##############
class Wheel
  attr_reader :rim, :tire
  def initialize(rim, tire)
    @rim       = rim
    @tire      = tire
  end

  def width   # <---- used to be 'diameter'
    rim + (tire * 2)
  end
# ...
end

############## Page 207 ##############
class Gear
  # ...
  def gear_inches
    ratio * wheel.diameter # <--- obsolete
  end
end

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

  def gear_inches
    ratio * wheel.diameter
  end

  def ratio
    chainring / cog.to_f
  end
# ...
end



############## Page 210 ##############
# Create a player of the 'Diameterizable' role
class DiameterDouble
  def diameter
    10
  end
end

class GearTest < MiniTest::Unit::TestCase
  def test_calculates_gear_inches
    gear =  Gear.new(
              chainring: 52,
              cog:       11,
              wheel:     DiameterDouble.new)

    assert_in_delta(47.27,
                    gear.gear_inches,
                    0.01)
  end
end

############## Page 212 ##############
class WheelTest < MiniTest::Unit::TestCase
  def setup
    @wheel = Wheel.new(26, 1.5)
  end

  def test_implements_the_diameterizable_interface
    assert_respond_to(@wheel, :diameter)
  end

  def test_calculates_diameter
    wheel = Wheel.new(26, 1.5)

    assert_in_delta(29,
                    wheel.diameter,
                    0.01)
  end
end