Getting HTTP 406 when trying to test facebooker application with cucumber

Question

I am trying to test facebook api calls with cucumber. Here is the code.

# app/controller/facebook_users_controller.rb

class FacebookUsersController < ApplicationController
  def create
    fb_user = facebook_session.user
    user = User.new(:facebook_uid => fb_user.uid, :facebook_session_key => facebook_session.session_key

    respond_to do |format|
      if user.save
        format.json { render :json => { :status => 'ok' }.to_json }
      end
    end
  end
end

# features/steps/facebook_connect_step.rb
Given /^I am a facebook connected user$/ do
  mock_session = Facebooker::MockSession.create

  post('/facebook_user.json')
  puts response.code
end

When I run the cucumber step for above step definition, I get a response code of 406 instead of 200. This happens in the cucumber test environment only and not in the browser(development/production). From logs, I can see that the user is getting saved.

I also run :set_facebook_session as a before filter in the application controller to make sure that a facebook session is available before trying to access it.