How to test ActiveRecord callbacks with RSpec?

Question

How to test the following example?

class Post < ActiveRecord::Base
  belongs_to :discussion, touch: true
end

Answer 1

You can set a message expectation:

it "should touch the discussion" do
  post = Factory.build(:post)
  post.discussion.should_receive(:touch)
  post.save!
end

This examples uses Factory Girl, but you could use fixtures or mocks as well.