Assigning cookies for test cases should now use cookies[], e.g:

  cookies[:email] = 'user@example.com'
  get :index
  assert_equal 'user@example.com', cookies[:email]

To clear the cookies, use clear, e.g:

  cookies.clear
  get :index
  assert_nil cookies[:email]

We now no longer write out HTTP_COOKIE and the cookie jar is
persistent between requests so if you need to manipulate the environment
for your test you need to do it before the cookie jar is created.