tests: move test/helpers to test/test_helpers.

The Rails convention is for test/helpers to be used for testing the view
helpers in app/helpers. We were using it to store certain utility
methods instead. Move these to test/test_helpers so that test/helpers
can be used for its intended purpose.

test/unit/pool_test.rb

@@ -1,11 +1,8 @@
 # encoding: utf-8
 
 require 'test_helper'
-require 'helpers/pool_archive_test_helper'
 
 class PoolTest < ActiveSupport::TestCase
-  include PoolArchiveTestHelper
-
   setup do
     Timecop.travel(1.month.ago) do
       @user = FactoryGirl.create(:user)