How to make fixtures updateable in Rails' tests?

Question

Below I listed some code from simple Rails application. The test listed below fails in last line, because the updated_at field of the post is not changed within the update action of PostController in this test. Why?

This behaviour seems to me a little strange, because standard timestamps are included in Post model, live testing on local server shows that this field is actually updated after returning from update action and first assertion is fulfilled thus it shows the update action went ok.

How can I make fixtures updateable in above meaning?

# app/controllers/post_controller.rb
def update
  @post = Post.find(params[:id])
  if @post.update_attributes(params[:post])
    redirect_to @post     # Update went ok!
  else
    render :action => "edit"
  end
end

# test/functional/post_controller_test.rb
test "should update post" do
  before = Time.now
  put :update, :id => posts(:one).id, :post => { :content => "anothercontent" }
  after = Time.now

  assert_redirected_to post_path(posts(:one).id)     # ok
  assert posts(:one).updated_at.between?(before, after), "Not updated!?" # failed
end

# test/fixtures/posts.yml
one:
  content: First post

Answer 1

posts(:one)

That means "fetch the fixture named ":one" in posts.yml. That's never going to change during a test, barring some extremely weird and destructive code that has no place in sane tests.

What you want to do is check the object that the controller is assigning.

post = assigns(:post)
assert post.updated_at.between?(before, after)

Answer 2

On a side note if you were using shoulda (http://www.thoughtbot.com/projects/shoulda/) it would look like this:

context "on PUT to :update" do
    setup do 
        @start_time = Time.now
        @post = posts(:one)
        put :update, :id => @post.id, :post => { :content => "anothercontent" } 
    end
    should_assign_to :post
    should "update the time" do
        @post.updated_at.between?(@start_time, Time.now)
    end
end

Shoulda is awesome.