gistfile1.rb

module A
  def foo1; end
end

class Klass
  include A
end

module B
  def foo2; end
end

module A
  include B
  def foo3; end
end

p Klass.instance_methods.include? :foo2
#has foo1 and foo3, but not foo2

class Klass2
  include A
end

p Klass2.instance_methods.include? :foo2
#has foo1, foo2, and foo3