Module include vs extend test. Developing a Rails engine and I want to add a method that all ActiveRecord objects will respond to when called. Refactored to use a single include

include-vs-extend.rb

require 'minitest/autorun'

module KnightIndustries
  def self.included (klass)
    klass.extend ClassMethods
  end
  
  def can_talk?
    false
  end
  
  module ClassMethods
    def built_by_knight
      include KnightIndustriesMethods
    end
  end
  
  module KnightIndustriesMethods
    def can_talk?
      true
    end
    
    def goes
      "Hello, Michael"
    end
  end
end

class Car
  def goes
    "Vroom Vroom"
  end
end

Car.send(:include, KnightIndustries)

class Kitt < Car
  built_by_knight
end

describe Car do
  before do
    @hyundai = Car.new
  end
  
  it "should not talk" do
    @hyundai.can_talk?.must_equal false
  end
  it "should say 'Vroom Vroom'" do
    @hyundai.goes.must_equal "Vroom Vroom"
  end
end

describe Kitt do
  before do
    @kitt = Kitt.new
  end
  
  it "should talk" do
    @kitt.can_talk?.must_equal true
  end
  it "should say 'Hello, Michael'" do
    @kitt.goes.must_equal "Hello, Michael"
  end
end