Adds polymorphic tests and documentation

test/adapter/polymorphic_test.rb

@@ -0,0 +1,72 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    module Adapter
+      class PolymorphicTest < ActiveSupport::TestCase
+        setup do
+          @employee = Employee.new(id: 42, name: 'Zoop Zoopler', email: 'zoop@example.com')
+          @picture = @employee.pictures.new(id: 1, title: 'headshot-1.jpg')
+          @picture.imageable = @employee
+
+          @attributes_serialization = serializable(@picture, serializer: PolymorphicBelongsToSerializer) # uses default adapter: attributes
+          @json_serialization = serializable(@picture, adapter: :json, serializer: PolymorphicBelongsToSerializer)
+          @json_api_serialization = serializable(@picture, adapter: :json_api, serializer: PolymorphicBelongsToSerializer)
+        end
+
+        def test_attributes_serialization
+          expected =
+            {
+              id: 1,
+              title: 'headshot-1.jpg',
+              imageable: {
+                id: 42,
+                name: 'Zoop Zoopler'
+              }
+            }
+
+          assert_equal(expected, @attributes_serialization.as_json)
+        end
+
+        def test_json_serializer
+          expected =
+            {
+              picture: {
+                id: 1,
+                title: 'headshot-1.jpg',
+                imageable: {
+                  id: 42,
+                  name: 'Zoop Zoopler'
+                }
+              }
+            }
+
+          assert_equal(expected, @json_serialization.as_json)
+        end
+
+        def test_json_api_serializer
+          expected =
+            {
+              data: {
+                id: '1',
+                type: 'pictures',
+                attributes: {
+                  title: 'headshot-1.jpg'
+                },
+                relationships: {
+                  imageable: {
+                    data: {
+                      id: '42',
+                      type: 'employees'
+                    }
+                  }
+                }
+              }
+            }
+
+          assert_equal(expected, @json_api_serialization.as_json)
+        end
+      end
+    end
+  end
+end