Testing Classes for Active Record Callbacks

mailing_list_updater_unit_test.rb

require 'test/unit'
require 'mocha'

# assumes MailingListUpdater is defined / exposed at the top level. this is not the case 
# for the code in this gist.

class MailingListUpdaterTest < Test::Unit::TestCase
  test "#update_mailing_list calls enqueue_for_mailing_list_update when a user is present" do
    user = mock('User', :enqueue_for_mailing_list_update => true)
    record = stub('Record')

    record.stubs(:user).returns(user)

    MailingListUpdater.new.update_mailing_list(record)
  end

  test "#update_mailing_list fails silently if a user is not present" do
    record = stub('Record')

    record.stubs(:user).returns(nil)

    assert_nothing_raised do
      MailingListUpdater.new.update_mailing_list(record)
    end
  end

  ...
end

model.rb

class Model
  class MailingListUpdater
    def initialize(user_proc = lambda { |record| record.user })
      @user_proc = user_proc
    end

    def user(record)
      @user_proc.call(record)
    end

    def update_mailing_list(record)
      return unless user(record)
      user(record).enqueue_for_mailing_list_update
    end

    alias_method :after_create, :update_mailing_list
    
    ...
  end

  after_create MailingListUpdater.new
end