extend_hierachy.rb

class A
  def test
    p "whatup from A"
  end
end
# => nil
module B
  def test
  p "whatup from B"
  super
  end
end
# => nil
a = A.new
# => #<A:0x112ba78>
a.test
# "whatup from A"
# => nil
a.extend B
# => #<A:0x112ba78>
a.test
# "whatup from B"
# "whatup from A"
# => nil