A rundown of the many ways to compare classes in Ruby.

class-comparison.rb

# coding: utf-8

require 'rspec' # 2.14.1

# NOTE: "include?" and "included_modules" are for modules only.
CLASS_METHODS = %i(
  !=
  <
  <=
  <=>
  ==
  ===
  >
  >=
  __id__
  ancestors
  eql?
  equal?
  include?
  included_modules
  inspect
  name
  object_id
  superclass
  to_s
)

def fake(klass)
  Class.new(BasicObject) do
    eigenclass = class << self; self end
    eigenclass.extend(Forwardable)
    eigenclass.def_delegators(klass, *CLASS_METHODS)

    define_method(:instance_of?) { |x| klass == x }
    define_method(:is_a?) { |x| klass >= x }
    alias_method(:kind_of?, :is_a?)
  end
end

describe Object do
  let(:fake_klass) { fake(described_class) }
  let(:fake_object) { fake_klass.new }
  let(:object) { described_class.new }

  %i(
    __id__
    ancestors
    included_modules
    inspect
    name
    object_id
    superclass
    to_s
  ).each do |method|
    it ".#{method}" do
      args = [method]
      expected = described_class.__send__(*args)
      actual = fake_klass.__send__(*args)
      expect(actual).to eql expected
    end
  end

  %i(
    !=
    <
    <=
    <=>
    ==
    >
    >=
    eql?
    equal?
  ).each do |method|
    it ".#{method}" do
      args = [method, described_class]
      expected = described_class.__send__(*args)
      actual = fake_klass.__send__(*args)
      expect(actual).to eql expected
    end
  end

  %i(
    include?
  ).each do |method|
    it ".#{method}" do
      args = [method, Comparable]
      expected = described_class.__send__(*args)
      actual = fake_klass.__send__(*args)
      expect(actual).to eql expected
    end
  end

  %i(
    ===
  ).each do |method|
    it ".#{method}" do
      [object, fake_object].each do |objekt|
        args = [method, objekt]
        expected = described_class.__send__(*args)
        actual = fake_klass.__send__(*args)
        expect(actual).to eql expected
      end
    end
  end

  %i(
    instance_of?
    is_a?
    kind_of?
  ).each do |method|
    it "##{method}" do
      args = [method, described_class]
      expected = object.__send__(*args)
      actual = fake_object.__send__(*args)
      expect(actual).to eql expected
    end
  end
end