test.rb

require 'test/unit'

module Stuff
  def self.included(base)
    base.extend Stuff::ClassMethods
  end

  module ClassMethods
    def foo
      'foo'
    end
  end

  def bar
    'bar'
  end
end

class A
  include Stuff
end

class ATest < Test::Unit::TestCase
  def test_a_has_bar
    assert_equal 'bar', A.new.bar
  end

  def test_A_has_foo
    assert_equal 'foo', A.foo
  end
end