diff --git a/test/support/isolated_unit.rb b/test/support/isolated_unit.rb
index 34f18661..d1d18eb6 100644
--- a/test/support/isolated_unit.rb
+++ b/test/support/isolated_unit.rb
@@ -46,6 +46,8 @@ require 'active_support/testing/isolation'
 
 module TestHelpers
   module Generation
+    module_function
+
     # Make a very basic app, without creating the whole directory structure.
     # Is faster and simpler than generating a Rails app in a temp directory
     def make_basic_app
diff --git a/test/support/rails_app.rb b/test/support/rails_app.rb
index 7f74e4ba..bc2fc8d1 100644
--- a/test/support/rails_app.rb
+++ b/test/support/rails_app.rb
@@ -1,27 +1,34 @@
-class ActiveModelSerializers::RailsApplication < Rails::Application
-  if Rails::VERSION::MAJOR >= 4
-    config.eager_load = false
+require 'support/isolated_unit'
+module ActiveModelSerializers
+  RailsApplication = TestHelpers::Generation.make_basic_app do |app|
+    app.configure do
+      config.secret_key_base = 'abc123'
+      config.active_support.test_order = :random
+      config.action_controller.perform_caching = true
+      ActionController::Base.cache_store = :memory_store
+    end
 
-    config.secret_key_base = 'abc123'
-
-    config.active_support.test_order = :random
-
-    config.logger = Logger.new(nil)
-
-    config.action_controller.perform_caching = true
-    ActionController::Base.cache_store = :memory_store
-
-    Rails.application.routes.default_url_options = { host: 'example.com' }
+    app.routes.default_url_options = { host: 'example.com' }
   end
 end
-ActiveModelSerializers::RailsApplication.initialize!
 
-module TestHelper
-  Routes = ActionDispatch::Routing::RouteSet.new
-  Routes.draw do
-    get ':controller(/:action(/:id))'
-    get ':controller(/:action)'
+Routes = ActionDispatch::Routing::RouteSet.new
+Routes.draw do
+  get ':controller(/:action(/:id))'
+  get ':controller(/:action)'
+end
+ActionController::Base.send :include, Routes.url_helpers
+ActionController::TestCase.class_eval do
+  def setup
+    @routes = Routes
   end
 
-  ActionController::Base.send :include, Routes.url_helpers
+  # For Rails5
+  # https://github.com/rails/rails/commit/ca83436d1b3b6cedd1eca2259f65661e69b01909#diff-b9bbf56e85d3fe1999f16317f2751e76L17
+  def assigns(key = nil)
+    warn "DEPRECATION: Calling 'assigns(#{key})' from #{caller[0]}"
+    assigns = {}.with_indifferent_access
+    @controller.view_assigns.each { |k, v| assigns.regular_writer(k, v) }
+    key.nil? ? assigns : assigns[key]
+  end
 end
diff --git a/test/support/test_case.rb b/test/support/test_case.rb
deleted file mode 100644
index 8f1afe79..00000000
--- a/test/support/test_case.rb
+++ /dev/null
@@ -1,19 +0,0 @@
-ActionController::TestCase.class_eval do
-  def setup
-    @routes = TestHelper::Routes
-  end
-
-  # For Rails5
-  # https://github.com/rails/rails/commit/ca83436d1b3b6cedd1eca2259f65661e69b01909#diff-b9bbf56e85d3fe1999f16317f2751e76L17
-  def assigns(key = nil)
-    assigns = {}.with_indifferent_access
-    @controller.view_assigns.each { |k, v| assigns.regular_writer(k, v) }
-    key.nil? ? assigns : assigns[key]
-  end
-
-  # Rails5: Uncomment for debugging where the warnings come from
-  # def non_kwarg_request_warning
-  #   super
-  #   STDOUT.puts caller[2..3]
-  # end
-end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 687bf0da..d0eba205 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -39,8 +39,6 @@ end
 
 require 'support/rails_app'
 
-require 'support/test_case'
-
 require 'support/serialization_testing'
 
 require 'support/rails5_shims'