Merge pull request #2464 from Shopify/0-9-stable-ac-test-case-lazy

[0.9 stable]  Avoid loading ActionController::TestCase in production

.github/workflows/ci.yml

@@ -75,3 +75,4 @@ jobs:
  bundle exec rake
  env:
  RAILS_VERSION: ${{ matrix.rails-version }}
+ RAILS_ENV: test

lib/active_model_serializers.rb

@@ -9,12 +9,22 @@
 begin
  require 'action_controller'
  require 'action_controller/serialization'
- require 'action_controller/serialization_test_case'
 
  ActiveSupport.on_load(:action_controller) do
  if ::ActionController::Serialization.enabled
  ActionController::Base.send(:include, ::ActionController::Serialization)
- ActionController::TestCase.send(:include, ::ActionController::SerializationAssertions)
+
+ # action_controller_test_case load hook was added in Rails 5.1
+ # https://github.com/rails/rails/commit/0510208dd1ff23baa619884c0abcae4d141fae53
+ if ActiveSupport::VERSION::STRING < '5.1'
+ require 'action_controller/serialization_test_case'
+ ActionController::TestCase.send(:include, ::ActionController::SerializationAssertions)
+ else
+ ActiveSupport.on_load(:action_controller_test_case) do
+ require 'action_controller/serialization_test_case'
+ ActionController::TestCase.send(:include, ::ActionController::SerializationAssertions)
+ end
+ end
  end
  end
 rescue LoadError