rspec users - Mar 2008 - Does one use mocks in stories?

My site is an external Facebook app. I need users to come to the start page and
if they are not already logged into their Facebook account (and have the app
installed) see a button to take them to the Facebook login/install page.

Using RFacebook, login is normally achieved with a before_filter. The user is 
sent to the Facebook login/install page and then the app redirects them back to 
one of my pages.

In a story, am I supposed to mock out that filter method to set the necessary 
variables and do the redirection or what? I haven''t seen any examples
that use
mocks in stories. Also am I right in thinking that if I am to mock this then I 
will need to use something like Mocha?

My initial draft looks like this:

Story ''An unlogged in user'', %{
   As an unlogged in user
   I want to log in to my Facebook account and start using MyApp
}, :type => RailsStory do

   Scenario ''starts at /'' do
     When ''arrive at /'' do
       get ''/''
     end

     Then ''the user should see the MyApp home page'' do
       response.should render_template(''/sessions/index'')
     end

     When ''the user clicks the log in/install button'' do
       post ''/''
     end

     Then ''the user should be redirected to the Facebook login/MyApp
install
page and on success back to their personal MyApp home page'' do
       ### What might go here???
     end
   end
end