Make serializer lookup configurable (#1757)

test/action_controller/lookup_proc_test.rb

@@ -0,0 +1,49 @@
+require 'test_helper'
+
+module ActionController
+  module Serialization
+    class LookupProcTest < ActionController::TestCase
+      module Api
+        module V3
+          class PostCustomSerializer < ActiveModel::Serializer
+            attributes :title, :body
+
+            belongs_to :author
+          end
+
+          class AuthorCustomSerializer < ActiveModel::Serializer
+            attributes :name
+          end
+
+          class LookupProcTestController < ActionController::Base
+            def implicit_namespaced_serializer
+              author = Author.new(name: 'Bob')
+              post = Post.new(title: 'New Post', body: 'Body', author: author)
+
+              render json: post
+            end
+          end
+        end
+      end
+
+      tests Api::V3::LookupProcTestController
+
+      test 'implicitly uses namespaced serializer' do
+        controller_namespace = lambda do |resource_class, _parent_serializer_class, namespace|
+          "#{namespace}::#{resource_class}CustomSerializer" if namespace
+        end
+
+        with_prepended_lookup(controller_namespace) do
+          get :implicit_namespaced_serializer
+
+          assert_serializer Api::V3::PostCustomSerializer
+
+          expected = { 'title' => 'New Post', 'body' => 'Body', 'author' => { 'name' => 'Bob' } }
+          actual = JSON.parse(@response.body)
+
+          assert_equal expected, actual
+        end
+      end
+    end
+  end
+end