Demonstration of behavior difference between Ruby 1.9.3 and 2.0+

test.rb

module A
  def foo
    puts "foo from A"
  end
end

class B
  include A

  def foo
    puts "foo from B"
    super
  end
end

class C < B
  alias_method :orig_foo, :foo

  def foo
    puts "foo from C"
    orig_foo
  end
end

class B
  alias_method :orig_foo, :foo

  def foo
    puts "foo from B (again)"
    orig_foo
  end
end

C.new.foo