default_locale.rb

# See http://stackoverflow.com/questions/1987354/how-to-set-locale-default-url-options-for-functional-tests-rails/8920258#8920258
class ActionController::TestCase
  module Behavior
    def process_with_default_locale(action, parameters = nil, session = nil, flash = nil, http_method = 'GET')
      parameters = { :locale => "en" }.merge( parameters || {} )
      process_without_default_locale(action, parameters, session, flash, http_method)
    end 
    alias_method_chain :process, :default_locale
  end 
end

class ActionView::TestCase::TestController
  def default_url_options(options={})
    { :locale => "en" }
  end
end

class ActionDispatch::Routing::RouteSet
  def default_url_options(options={})
    { :locale => "en" }
  end
end