Define the configuration at Active Support

activesupport/lib/active_support.rb

@@ -70,6 +70,16 @@ module ActiveSupport
 
     NumberHelper.eager_load!
   end
+
+  @@test_order = nil
+
+  def self.test_order=(new_order)
+    @@test_order = new_order
+  end
+
+  def self.test_order
+    @@test_order
+  end
 end
 
 autoload :I18n, "active_support/i18n"

activesupport/lib/active_support/test_case.rb

@@ -12,22 +12,18 @@ require 'active_support/core_ext/kernel/reporting'
 require 'active_support/deprecation'
 
 module ActiveSupport
-  class << self
-    delegate :test_order, :test_order=, to: :'ActiveSupport::TestCase'
-  end
-
   class TestCase < ::Minitest::Test
     Assertion = Minitest::Assertion
 
-    @@test_order = nil
-
     class << self
       def test_order=(new_order)
-        @@test_order = new_order
+        ActiveSupport.test_order = new_order
       end
 
       def test_order
-        if @@test_order.nil?
+        test_order = ActiveSupport.test_order
+
+        if test_order.nil?
           ActiveSupport::Deprecation.warn "You did not specify a value for the " \
             "configuration option 'active_support.test_order'. In Rails 5.0, " \
             "the default value of this option will change from `:sorted` to " \
@@ -42,10 +38,11 @@ module ActiveSupport
             "Alternatively, you can opt into the future behavior by setting this " \
             "option to `:random`."
 
-          @@test_order = :sorted
+          test_order = :sorted
+          self.test_order = test_order
         end
 
-        @@test_order
+        test_order
       end
 
       alias :my_tests_are_order_dependent! :i_suck_and_my_tests_are_order_dependent!

railties/test/configuration/middleware_stack_proxy_test.rb

@@ -1,3 +1,4 @@
+require 'active_support'
 require 'active_support/testing/autorun'
 require 'rails/configuration'
 require 'active_support/test_case'

railties/test/isolation/abstract_unit.rb

@@ -9,6 +9,7 @@
 require 'fileutils'
 
 require 'bundler/setup' unless defined?(Bundler)
+require 'active_support'
 require 'active_support/testing/autorun'
 require 'active_support/test_case'