Problem testing controller

Hello, I'm very new with Ruby (and Rails), but I need to make a test
with testcase.
I made an application that use openid login (following Ryan Bates's
tutorial), where the session controller code is:

def create
  if using_open_id?
    open_id_authentication(params[:openid_url])
  ...
  end
end

protected
def open_id_authentication(openid_url)
  authenticate_with_open_id(...) do |result, identity_url, registration|
    if result.successful?
    ...
    end
  end
end

I tried to create a stub with no luck (maybe I don't really know how it
works). I'd like to test the 'authenticate_with_open_id' block,
currently I'm using simplecov to check the coverage and stops in that
line.

Thanks