do not require a file that is not used

activerecord/test/cases/helper.rb

@@ -7,6 +7,7 @@ require 'stringio'
 require 'mocha'
 
 require 'active_record'
+require 'active_record/test_case'
 require 'active_support/dependencies'
 require 'active_support/logger'
 

railties/lib/rails/test_help.rb

@@ -25,8 +25,6 @@ if defined?(MiniTest)
 end
 
 if defined?(ActiveRecord::Base)
-  require 'active_record/test_case'
-
   class ActiveSupport::TestCase
     include ActiveRecord::TestFixtures
     self.fixture_path = "#{Rails.root}/test/fixtures/"