Use the Test namespace

lib/active_model/serializable_resource.rb

@@ -15,7 +15,6 @@ def initialize(resource, options = {})
       @resource = resource
       @adapter_opts, @serializer_opts =
         options.partition { |k, _| ADAPTER_OPTION_KEYS.include? k }.map { |h| Hash[h] }
-      notify_active_support
     end
 
     def serialization_scope=(scope)
@@ -68,13 +67,6 @@ def serializer?
 
     protected
 
-    def notify_active_support
-      return unless serializer?
-      event_name = 'serialize.active_model_serializers'
-      payload = { serializer: serializer.name }
-      ActiveSupport::Notifications.instrument(event_name, payload)
-    end
-
     attr_reader :resource, :adapter_opts, :serializer_opts
   end
 end

lib/active_model/serializer/railtie.rb

@@ -19,5 +19,7 @@ class Railtie < Rails::Railtie
       app.load_generators
       require 'generators/serializer/resource_override'
     end
+
+    ActionController::TestCase.send(:include, ActiveModelSerializers::Test::Serializer)
   end
 end

lib/active_model_serializers.rb

@@ -51,7 +51,7 @@ def silence_warnings
 require 'active_model/serializer'
 require 'active_model/serializable_resource'
 require 'active_model/serializer/version'
-require 'active_model/serializer/assertions'
+require 'active_model_serializers/test/serializer'
 
 require 'action_controller/serialization'
 ActiveSupport.on_load(:action_controller) do
@@ -60,7 +60,6 @@ def silence_warnings
   ActionDispatch::Reloader.to_prepare do
     ActiveModel::Serializer.serializers_cache.clear
   end
-  ActionController::TestCase.send(:include, ActiveModel::Serializer::Assertions)
 end
 
 require 'active_model/serializer/railtie'

lib/active_model/serializer/assertions.rb → lib/active_model_serializers/test/serializer.rb

@@ -1,6 +1,6 @@
-module ActiveModel
-  class Serializer
-    module Assertions
+module ActiveModelSerializers
+  module Test
+    module Serializer
       extend ActiveSupport::Concern
 
       included do
@@ -60,7 +60,7 @@ def assert_serializer(expectation, message = nil)
       def setup_serialization_subscriptions
         @serializers = []
         ActiveSupport::Notifications.subscribe(event_name) do |_name, _start, _finish, _id, payload|
-          serializer = payload[:serializer]
+          serializer = payload[:serializer].name
           serializers << serializer
         end
       end
@@ -70,7 +70,7 @@ def teardown_serialization_subscriptions
       end
 
       def event_name
-        'serialize.active_model_serializers'
+        'render.active_model_serializers'
       end
 
       def matches_class?(expectation)

test/assertions_test.rb → test/active_model_serializers/test/serializer_test.rb

@@ -1,8 +1,8 @@
 require 'test_helper'
 
-module ActiveModel
-  class Serializer
-    class AssertionsTest < ActionController::TestCase
+module ActiveModelSerializers
+  module Test
+    class SerializerTest < ActionController::TestCase
       class MyController < ActionController::Base
         def render_using_serializer
           render json: Profile.new(name: 'Name 1', description: 'Description 1', comments: 'Comments 1')