guard_rail_spec.rb

context "making sure we don't accidentally take the site down" do
  EXPECTED_NUMBER_OF_WORKERS = 10  # copy this value from the other place it's defined; this shouldn't be dynamic, repeating yourself is better

  it "reminds the user of side effects" do
   begin
     expect(MySystem::NUMBER_OF_WORKERS).to eq(EXPECTED_NUMBER_OF_WORKERS)
    rescue RSpec::Expectations::ExpectationNotMetError => error
      error.message << "\n"
      error.message << <<~HEREDOC
        📎 Oh hi there! It looks like you changed the value of MySystem::NUMBER_OF_WORKERS.

        This constant is used to determine how many workers should process a job from the queue
        at any given time, so changing it has some very meaningful side effects.

        If this is what you intended - great! Update this test with the new value and you're good to go.

        If it's not what you intended - please set the value back to #{EXPECTED_NUMBER_OF_WORKERS}.
      HEREDOC

      raise error
    end
  end
end