billing_module.rb

# this could be in a folder with other modules 'lib/sites/ecom/pages/checkout/' 

module Ecom
  class CheckoutPage < ::Taza::Site
    filter :billing_ready?, :billing

    page_module :billing do
      element(:first_name) { browser.text_field(:id => 'billing_first_name') }
    end

    def billing_ready?
      true
    end
  end
end

checkout_spec.rb

# This could even be split into multiple files in a 'checkout' folder

describe 'Checkout Page' do
  describe 'Billing Module' do
    Ecom.new do |ecom|
      ecom.checkout_page(:billing) do |b|
        b.first_name.set 'John'
      end
    end
  end

  describe 'Shipping Module' do
    Ecom.new do |ecom|
      ecom.checkout_page(:shipping) do |s|
        s.first_name.set 'John'
      end
    end
  end
end

shipping_module.rb

# this could be in a folder with other modules 'lib/sites/ecom/pages/checkout/'

module Ecom
  class CheckoutPage < ::Taza::Site
    filter :shipping_ready?, :shipping

    page_module :shipping do
      element(:first_name) { browser.text_field(:id => 'shipping_first_name') }
    end

    def shipping_ready?
      true
    end
  end
end