How to get/set session in ActionView::TestCase?

Hi,

I'm trying to use Rails 2.1 ActionView::TestCase to test my helpers.

I got really simple method in ApplicationHelper:

def current_user
  User.find(session[:user_id])
end

How can I set/get session in ActionView::TestCase? It looks similar to
functional tests - there's ActionView::TestCase::TestController, which
has request and response, but session object seems to be just an empty
array.