Including SessionsHelper in RailsTutorial.org test_helper: why not?

In railstutorial.org, Listing 8.23:

ENV['RAILS_ENV'] ||= 'test'
.
.
.
class ActiveSupport::TestCase
  fixtures :all

  # Returns true if a test user is logged in.
  def is_logged_in?
    !session[:user_id].nil?
  end
end

suggests creating a duplicate method to check whether the current user is logged in (having already defined such a method in sessions_helper.rb) for use in testing. However, I was wondering why the author chose to do this in the first place. He explains his reasoning as such:

To test the behavior from Listing 8.22, we can add a line to the test from Listing 7.26 to check that the user is logged in. It’s helpful in this context to define a is_logged_in? helper method to parallel the logged_in? helper defined in Listing 8.15, which returns true if there’s a user id in the (test) session and false otherwise (Listing 8.23). (Because helper methods aren’t available in tests, we can’t use the current_user as in Listing 8.15, but the session method is available, so we use that instead.) Here we use is_logged_in? instead of logged_in? so that the test helper and Sessions helper methods have different names, which prevents them from being mistaken for each other.

However, in an exercise from Chapter 5, the author writes code including ApplicationHelper in its test suite (see Listing 5.37):

ENV['RAILS_ENV'] ||= 'test'
.
.
.
class ActiveSupport::TestCase
  fixtures :all
  include ApplicationHelper
  .
  .
  .
end

When I included SessionsHelper and ran my tests using code from that helper module, my tests still passed. I was wondering if the author chose to forgo including SessionsHelper in the code because that technique was used in an exercise (and thus better off applied elsewhere) or if actually including SessionsHelper to the test suite is a Bad Thing for some reason or another. Any insights to this?