fix rubocop; start new testing pattern

lib/active_model_serializers/lookup_chain.rb

@@ -1,6 +1,5 @@
 module ActiveModelSerializers
   module LookupChain
-
     # Standard appending of Serializer to the resource name.
     #
     # Example:

test/feature/configuration/serializer_lookup/using_serializable_resource_test.rb

@@ -0,0 +1,42 @@
+require 'test_helper'
+
+describe 'feature' do
+  describe 'configuration' do
+    describe 'serializer lookup' do
+      describe 'using SerializableResource' do
+        it 'uses the child serializer' do
+          class Parent < ::Model; end
+          class Child < ::Model; end
+
+          class ParentSerializer < ActiveModel::Serializer
+            class ChildSerializer < ActiveModel::Serializer
+              attributes :name, :child_attr
+              def child_attr
+                true
+              end
+            end
+
+            attributes :name
+            belongs_to :child
+          end
+
+          parent = Parent.new(name: 'parent', child: Child.new(name: 'child'))
+          resource = ActiveModelSerializers::SerializableResource.new(
+            parent,
+            adapter: :attributes
+          )
+
+          expected = {
+            name: 'parent',
+            child: {
+              name: 'child',
+              child_attr: true
+            }
+          }
+
+          assert_equal expected, resource.serializable_hash
+        end
+      end
+    end
+  end
+end