Centro lightning talk on different ways to use Ruby modules

lightning.rb

module Alcoholic
  def abv
    4.2
  end
end

class Lager
  include Alcoholic
end

class Ipa
  include Alcoholic

  def abv
    6.0
  end
end

module DoubleHopped
  def abv
    8.3
  end
end

lightning_spec.rb

require_relative 'spec_helper'

RSpec.describe 'Ruby Modules' do
  let(:ipa_abv) { 6.0 }
  let(:double_hopped_abv) { 8.3 }

  def print_ancestors(klass = Ipa)
    puts "\n** #{klass.name} Ancestors: #{klass.ancestors}"
  end

  specify "a class can override module-defined methods" do
    expect(Ipa.new.abv).to eq ipa_abv
    print_ancestors
  end

  specify "a module cannot override class-defined instance methods using .include" do
    Ipa.send :include, DoubleHopped
    print_ancestors
    expect(Ipa.new.abv).to eq ipa_abv
  end

  specify "as of Ruby 2.0 a module can override class-defined instance methods using .prepend" do
    Ipa.send :prepend, DoubleHopped
    print_ancestors
    expect(Ipa.new.abv).to eq double_hopped_abv
  end

  specify "a module can override module-defined methods" do
    Lager.send :include, DoubleHopped
    print_ancestors Lager
    expect(Lager.new.abv).to eq double_hopped_abv
  end

  specify "an instance can be extended with a module to override its instance methods" do
    ipa = Ipa.new
    expect(ipa.abv).to eq ipa_abv
    ipa.extend DoubleHopped
    expect(ipa.abv).to eq double_hopped_abv
  end
end

spec_helper.rb

# See http://rubydoc.info/gems/rspec-core/RSpec/Core/Configuration
RSpec.configure do |config|
  # rspec-expectations config goes here. You can use an alternate
  # assertion/expectation library such as wrong or the stdlib/minitest
  # assertions if you prefer.
  config.expect_with :rspec do |expectations|
    # This option will default to `true` in RSpec 4. It makes the `description`
    # and `failure_message` of custom matchers include text for helper methods
    # defined using `chain`, e.g.:
    #     be_bigger_than(2).and_smaller_than(4).description
    #     # => "be bigger than 2 and smaller than 4"
    # ...rather than:
    #     # => "be bigger than 2"
    expectations.include_chain_clauses_in_custom_matcher_descriptions = true
  end

  # rspec-mocks config goes here. You can use an alternate test double
  # library (such as bogus or mocha) by changing the `mock_with` option here.
  config.mock_with :rspec do |mocks|
    # Prevents you from mocking or stubbing a method that does not exist on
    # a real object. This is generally recommended, and will default to
    # `true` in RSpec 4.
    mocks.verify_partial_doubles = true
  end

# The settings below are suggested to provide a good initial experience
# with RSpec, but feel free to customize to your heart's content.

  # These two settings work together to allow you to limit a spec run
  # to individual examples or groups you care about by tagging them with
  # `:focus` metadata. When nothing is tagged with `:focus`, all examples
  # get run.
  config.filter_run :focus
  config.run_all_when_everything_filtered = true

  # Limits the available syntax to the non-monkey patched syntax that is
  # recommended. For more details, see:
  #   - http://myronmars.to/n/dev-blog/2012/06/rspecs-new-expectation-syntax
  #   - http://www.teaisaweso.me/blog/2013/05/27/rspecs-new-message-expectation-syntax/
  #   - http://myronmars.to/n/dev-blog/2014/05/notable-changes-in-rspec-3#new__config_option_to_disable_rspeccore_monkey_patching
  config.disable_monkey_patching!

  # Many RSpec users commonly either run the entire suite or an individual
  # file, and it's useful to allow more verbose output when running an
  # individual spec file.
  if config.files_to_run.one?
    # Use the documentation formatter for detailed output,
    # unless a formatter has already been configured
    # (e.g. via a command-line flag).
    config.default_formatter = 'doc'
  end

  # don't run random for lightening talk
  config.order = :defined

  # make sure modified classes are restored after each spec run
  config.before(:each) { load 'lightning.rb' }

  config.after(:each) do
    %i{Ipa Lager Alcoholic DoubleHopped}.each do |const|
      Object.send :remove_const, const
    end
  end
end