Explicitly require files before monkey patching them.

railties/lib/rails/test_help.rb

@@ -4,14 +4,18 @@
 
 require 'test/unit'
 require 'active_support/core_ext/kernel/requires'
+require 'active_support/test_case'
+require 'action_controller/test_case'
+require 'action_dispatch/testing/integration'
 
-# TODO: Figure out how to get the Rails::BacktraceFilter into minitest/unit
 if defined?(Test::Unit::Util::BacktraceFilter) && ENV['BACKTRACE'].nil?
   require 'rails/backtrace_cleaner'
   Test::Unit::Util::BacktraceFilter.module_eval { include Rails::BacktraceFilterForTestUnit }
 end
 
 if defined?(ActiveRecord)
+  require 'active_record/test_case'
+
   class ActiveSupport::TestCase
     include ActiveRecord::TestFixtures
     self.fixture_path = "#{Rails.root}/test/fixtures/"