Bring back assert_serializer

The `assert_serializer` test helper was removed at some point.

This patch brings back the `assert_serializer` test helper. This is the last
revision[1] that has the helper. The original helper was used as base.

[1]: https://github.com/rails-api/active_model_serializers/tree/610aeb2e9297fa31b8d561f0be9a4597f0258f8c

CHANGELOG.md

@@ -17,6 +17,7 @@ Features:
 - [#1158](https://github.com/rails-api/active_model_serializers/pull/1158) Add support for wildcards in `include` option (@beauby)
 - [#1127](https://github.com/rails-api/active_model_serializers/pull/1127) Add support for nested
     associations for JSON and Attributes adapters via the `include` option (@NullVoxPopuli, @beauby).
+- [#1099](https://github.com/rails-api/active_model_serializers/pull/1099) Adds `assert_serializer` test helper (@maurogeorge)
 
 Fixes:
 

docs/README.md

@@ -15,6 +15,7 @@ This is the documentation of AMS, it's focused on the **0.10.x version.**
 - [How to add root key](howto/add_root_key.md)
 - [How to add pagination links](howto/add_pagination_links.md)
 - [Using AMS Outside Of Controllers](howto/outside_controller_use.md)
+- [Testing AMS](howto/test.md)
 
 ## Getting Help
 

docs/howto/test.md

@@ -0,0 +1,29 @@
+# How to test
+
+## Test helpers
+
+AMS provides a `assert_serializer` method to be used on your controller tests to
+assert that a specific serializer was used.
+
+```ruby
+class PostsControllerTest < ActionController::TestCase
+  test "should render post serializer" do
+    get :index
+    assert_serializer "PostSerializer"
+    #  # return a custom error message
+    #  assert_serializer "PostSerializer", "PostSerializer not rendered"
+    #
+    #  # assert that the instance of PostSerializer was rendered
+    #  assert_serializer PostSerializer
+    #
+    #  # assert that the "PostSerializer" serializer was rendered
+    #  assert_serializer :post_serializer
+    #
+    #  # assert that the rendered serializer starts with "Post"
+    #  assert_serializer %r{\APost.+\Z}
+    #
+    #  # assert that no serializer was rendered
+    #  assert_serializer nil
+  end
+end
+```

lib/active_model/serializable_resource.rb

@@ -9,6 +9,7 @@ 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
 
     delegate :serializable_hash, :as_json, :to_json, to: :adapter
@@ -61,6 +62,13 @@ def serializer?
       use_adapter? && !!(serializer)
     end
 
+    def notify_active_support
+      return unless serializer?
+      event_name = 'serialize.active_model_serializers'
+      payload = { serializer: serializer.name }
+      ActiveSupport::Notifications.instrument(event_name, payload)
+    end
+
     private
 
     ActiveModelSerializers.silence_warnings do

lib/active_model/serializer/assertions.rb

@@ -0,0 +1,104 @@
+module ActiveModel
+  class Serializer
+    module Assertions
+      extend ActiveSupport::Concern
+
+      included do
+        setup :setup_serialization_subscriptions
+        teardown :teardown_serialization_subscriptions
+      end
+
+      # Asserts that the request was rendered with the appropriate serializers.
+      #
+      #  # assert that the "PostSerializer" serializer was rendered
+      #  assert_serializer "PostSerializer"
+      #
+      #  # return a custom error message
+      #  assert_serializer "PostSerializer", "PostSerializer not rendered"
+      #
+      #  # assert that the instance of PostSerializer was rendered
+      #  assert_serializer PostSerializer
+      #
+      #  # assert that the "PostSerializer" serializer was rendered
+      #  assert_serializer :post_serializer
+      #
+      #  # assert that the rendered serializer starts with "Post"
+      #  assert_serializer %r{\APost.+\Z}
+      #
+      #  # assert that no serializer was rendered
+      #  assert_serializer nil
+      #
+      def assert_serializer(expectation, message = nil)
+        # Force body to be read in case the template is being streamed.
+        response.body
+
+        msg = message || "expecting <#{expectation.inspect}> but rendering with <#{serializers}>"
+
+        matches_serializer = case expectation
+                             when a_serializer?
+                               matches_class?(expectation)
+                             when Symbol
+                               matches_symbol?(expectation)
+                             when String
+                               matches_string?(expectation)
+                             when Regexp
+                               matches_regexp?(expectation)
+                             when NilClass
+                               matches_nil?
+                             else
+                               fail ArgumentError, 'assert_serializer only accepts a String, Symbol, Regexp, ActiveModel::Serializer, or nil'
+                             end
+        assert(matches_serializer, msg)
+      end
+
+      private
+
+      ActiveModelSerializers.silence_warnings do
+        attr_reader :serializers, :expectation
+      end
+
+      def setup_serialization_subscriptions
+        @serializers = []
+        ActiveSupport::Notifications.subscribe(event_name) do |_name, _start, _finish, _id, payload|
+          serializer = payload[:serializer]
+          serializers << serializer
+        end
+      end
+
+      def teardown_serialization_subscriptions
+        ActiveSupport::Notifications.unsubscribe(event_name)
+      end
+
+      def event_name
+        'serialize.active_model_serializers'
+      end
+
+      def matches_class?(expectation)
+        serializers.include?(expectation.name)
+      end
+
+      def matches_symbol?(expectation)
+        expectation = expectation.to_s.camelize
+        serializers.include?(expectation)
+      end
+
+      def matches_string?(expectation)
+        !expectation.empty? && serializers.include?(expectation)
+      end
+
+      def matches_regexp?(expectation)
+        serializers.any? do |serializer|
+          serializer.match(expectation)
+        end
+      end
+
+      def matches_nil?
+        serializers.blank?
+      end
+
+      def a_serializer?
+        ->(exp) { exp.is_a?(Class) && exp < ActiveModel::Serializer }
+      end
+    end
+  end
+end

lib/active_model_serializers.rb

@@ -42,13 +42,15 @@ def silence_warnings
 require 'active_model/serializer'
 require 'active_model/serializable_resource'
 require 'active_model/serializer/version'
+require 'active_model/serializer/assertions'
 
 require 'action_controller/serialization'
 ActiveSupport.on_load(:action_controller) do
   include ::ActionController::Serialization
   ActionDispatch::Reloader.to_prepare do
     ActiveModel::Serializer.serializers_cache.clear
   end
+  ActionController::TestCase.send(:include, ActiveModel::Serializer::Assertions)
 end
 
 require 'active_model/serializer/railtie'

test/assertions_test.rb

@@ -0,0 +1,70 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class AssertionsTest < ActionController::TestCase
+      class MyController < ActionController::Base
+        def render_using_serializer
+          render json: Profile.new(name: 'Name 1', description: 'Description 1', comments: 'Comments 1')
+        end
+
+        def render_text
+          render text: 'ok'
+        end
+
+        def render_template
+          prepend_view_path './test/fixtures'
+          render template: 'template'
+        end
+      end
+
+      tests MyController
+
+      def test_supports_specifying_serializers_with_a_serializer_class
+        get :render_using_serializer
+        assert_serializer ProfileSerializer
+      end
+
+      def test_supports_specifying_serializers_with_a_regexp
+        get :render_using_serializer
+        assert_serializer(/\AProfile.+\Z/)
+      end
+
+      def test_supports_specifying_serializers_with_a_string
+        get :render_using_serializer
+        assert_serializer 'ProfileSerializer'
+      end
+
+      def test_supports_specifying_serializers_with_a_symbol
+        get :render_using_serializer
+        assert_serializer :profile_serializer
+      end
+
+      def test_supports_specifying_serializers_with_a_nil
+        get :render_text
+        assert_serializer nil
+      end
+
+      def test_raises_descriptive_error_message_when_serializer_was_not_rendered
+        get :render_using_serializer
+        e = assert_raise ActiveSupport::TestCase::Assertion do
+          assert_serializer 'PostSerializer'
+        end
+        assert_match 'expecting <"PostSerializer"> but rendering with <["ProfileSerializer"]>', e.message
+      end
+
+      def test_raises_argument_error_when_asserting_with_invalid_object
+        get :render_using_serializer
+        e = assert_raise ArgumentError do
+          assert_serializer Hash
+        end
+        assert_match 'assert_serializer only accepts a String, Symbol, Regexp, ActiveModel::Serializer, or nil', e.message
+      end
+
+      def test_does_not_overwrite_notification_subscriptions
+        get :render_template
+        assert_template 'template'
+      end
+    end
+  end
+end

test/fixtures/template.html.erb

@@ -0,0 +1 @@
+<p>Hello.</p>