module_test.rb

require 'test_helper'

module ::TestModule
  def self.extended(base)
    add_properties_to base
  end

  def self.included(base)
    add_properties_to base
  end

  def self.add_properties_to(base)
    base.class_eval do
      before_create :set_payment_id
    end
  end
end

class ModuleTest < ActiveSupport::TestCase
  setup do
    klass = Class.new do
      extend ActiveModel::Callbacks

      define_model_callbacks :create, :before

      attr_reader :payment_id

      def create
        run_callbacks :create
      end

      private

      def set_payment_id
        @payment_id = 1
      end
    end

    @object = klass.new
    @object.extend TestModule
  end

  test 'payment id is set to 1' do
    @object.create

    assert_equal 1, @object.payment_id
  end
end