How to unit test a presenter using rails i18n and ActionView helpers *without* loading the spec_helper, hence keeping the tests fast?

fast_presenter_spec.rb

require 'action_view/helpers/number_helper'
require 'rails-i18n'

class FastPresenter
  include ActionView::Helpers::NumberHelper

  def initialize(value)
    @value = value
  end

  def decorate
    number_to_percentage @value, precision: 2
  end

end

describe FastPresenter do

  before do
    load_rails_i18n :fr
    I18n.default_locale = :fr

    @presenter = FastPresenter.new 10
  end

  it "decorates as a percentage
          with 2 digits after the decimal separator (locallized!)" do
    expect(@presenter.decorate).to eq("10,00%")
  end

  # Helpers: move these to a support file
  def load_rails_i18n(pattern)
    RailsI18n::Railtie.add("rails/locale/#{pattern}.yml")
    RailsI18n::Railtie.add("rails/pluralization/#{pattern}.rb")
    RailsI18n::Railtie.add("rails/transliteration/#{pattern}.{rb,yml}")

    RailsI18n::Railtie.init_pluralization_module
  end

  def load_rails_app_config_locales
    # /!\ RAILS root is a relative path
    rails_root = Pathname.new(File.expand_path("../../..", __FILE__))
    I18n.load_path += Dir[rails_root.join('config', 'locales', '*.{rb,yml}')]
  end
  
end

I18n.load_path?

Benchmark

With spec_helper

time rspec spec/lib/fast_presenter_spec.rb
.

Finished in 0.05301 seconds
1 example, 0 failures

real 0m10.430s
user 0m7.715s
sys 0m1.579s

Fast tests

ruby-1.9.3-p327$ time rspec spec/lib/fast_presenter_spec.rb
.

Finished in 0.01953 seconds
1 example, 0 failures

real 0m1.323s
user 0m1.111s
sys 0m0.177s