Reorganize autoloads:

  * A new module (ActiveSupport::Autoload) is provide that extends
    autoloading with new behavior.
  * All autoloads in modules that have extended ActiveSupport::Autoload
    will be eagerly required in threadsafe environments
  * Autoloads can optionally leave off the path if the path is the same
    as full_constant_name.underscore
  * It is possible to specify that a group of autoloads live under an
    additional path. For instance, all of ActionDispatch's middlewares
    are ActionDispatch::MiddlewareName, but they live under 
    "action_dispatch/middlewares/middleware_name"
  * It is possible to specify that a group of autoloads are all found
    at the same path. For instance, a number of exceptions might all
    be declared there.
  * One consequence of this is that testing-related constants are not
    autoloaded. To get the testing helpers for a given component,
    require "component_name/test_case". For instance, "action_controller/test_case".
  * test_help.rb, which is automatically required by a Rails application's
    test helper, requires the test_case.rb for all active components, so
    this change will not be disruptive in existing or new applications.

3 files changed, 25 insertions, 20 deletions

diff --git a/activemodel/lib/active_model.rb b/activemodel/lib/active_model.rb
index 505e16c195..8e14b6724f 100644
--- a/activemodel/lib/active_model.rb
+++ b/activemodel/lib/active_model.rb
@@ -26,28 +26,31 @@ $:.unshift(activesupport_path) if File.directory?(activesupport_path)
 require 'active_support'
 
 module ActiveModel
-  autoload :AttributeMethods, 'active_model/attribute_methods'
-  autoload :Conversion, 'active_model/conversion'
-  autoload :DeprecatedErrorMethods, 'active_model/deprecated_error_methods'
-  autoload :Dirty, 'active_model/dirty'
-  autoload :Errors, 'active_model/errors'
-  autoload :Lint, 'active_model/lint'
-  autoload :Name, 'active_model/naming'
-  autoload :Naming, 'active_model/naming'
-  autoload :Observer, 'active_model/observing'
-  autoload :Observing, 'active_model/observing'
-  autoload :Serialization, 'active_model/serialization'
-  autoload :StateMachine, 'active_model/state_machine'
-  autoload :TestCase, 'active_model/test_case'
-  autoload :Translation, 'active_model/translation'
-  autoload :Validations, 'active_model/validations'
-  autoload :ValidationsRepairHelper, 'active_model/validations_repair_helper'
-  autoload :Validator, 'active_model/validator'
-  autoload :VERSION, 'active_model/version'
+  extend ActiveSupport::Autoload
+
+  autoload :AttributeMethods
+  autoload :Conversion
+  autoload :DeprecatedErrorMethods
+  autoload :Dirty
+  autoload :Errors
+  autoload :Lint
+  autoload :Name,         'active_model/naming'
+  autoload :Naming
+  autoload :Observer,     'active_model/observing'
+  autoload :Observing
+  autoload :Serialization
+  autoload :StateMachine
+  autoload :Translation
+  autoload :Validations
+  autoload :ValidationsRepairHelper
+  autoload :Validator
+  autoload :VERSION
 
   module Serializers
-    autoload :JSON, 'active_model/serializers/json'
-    autoload :Xml, 'active_model/serializers/xml'
+    extend ActiveSupport::Autoload
+
+    autoload :JSON
+    autoload :Xml
   end
 end
 
diff --git a/activemodel/test/cases/helper.rb b/activemodel/test/cases/helper.rb
index c1a3f6a4a7..024f2378be 100644
--- a/activemodel/test/cases/helper.rb
+++ b/activemodel/test/cases/helper.rb
@@ -10,6 +10,7 @@ $:.unshift(lib) unless $:.include?('lib') || $:.include?(lib)
 
 require 'config'
 require 'active_model'
+require 'active_model/test_case'
 
 # Show backtraces for deprecated behavior for quicker cleanup.
 ActiveSupport::Deprecation.debug = true
diff --git a/activemodel/test/cases/tests_database.rb b/activemodel/test/cases/tests_database.rb
index 8dd00ea147..79668dd941 100644
--- a/activemodel/test/cases/tests_database.rb
+++ b/activemodel/test/cases/tests_database.rb
@@ -2,6 +2,7 @@ require 'logger'
 
 $:.unshift(File.dirname(__FILE__) + '/../../../activerecord/lib')
 require 'active_record'
+require 'active_record/test_case'
 require 'active_record/fixtures'
 
 module ActiveModel