In order to have a transition path to this coming big change, it was decided to have a magic comment at the beginning of files, so you can use in Ruby 2.x. To do so, just add this comment in the first line of your files:
# frozen_string_literal: true class YourClass # ... end
Try adding it to your
rails_helper file and let me know in the comments if your performance gets any better.
More info: Ruby issue #8976.