Follow up to #1535

- The removed classes and modules were added back with deprecation
  warning and deprecation test were added for them.
- One test was renamed because it contained `__`.
- Some tests were refactored.
- The ActiveModelSerializers::Deserialization module is now called
  Adapter instead of ActiveModelSerializers::Adapter.
- The changelog was added for #1535

test/adapter/json_api/resource_identifier_test.rb

@@ -0,0 +1,85 @@
+require 'test_helper'
+
+module ActiveModelSerializers
+  module Adapter
+    class JsonApi
+      class ResourceIdentifierTest < ActiveSupport::TestCase
+        class WithDefinedTypeSerializer < ActiveModel::Serializer
+          type 'with_defined_type'
+        end
+
+        class WithDefinedIdSerializer < ActiveModel::Serializer
+          def id
+            'special_id'
+          end
+        end
+
+        class FragmentedSerializer < ActiveModel::Serializer; end
+
+        setup do
+          @model = Author.new(id: 1, name: 'Steve K.')
+          ActionController::Base.cache_store.clear
+        end
+
+        def test_defined_type
+          test_type(WithDefinedTypeSerializer, 'with_defined_type')
+        end
+
+        def test_singular_type
+          test_type_inflection(AuthorSerializer, 'author', :singular)
+        end
+
+        def test_plural_type
+          test_type_inflection(AuthorSerializer, 'authors', :plural)
+        end
+
+        def test_id_defined_on_object
+          test_id(AuthorSerializer, @model.id.to_s)
+        end
+
+        def test_id_defined_on_serializer
+          test_id(WithDefinedIdSerializer, 'special_id')
+        end
+
+        def test_id_defined_on_fragmented
+          FragmentedSerializer.fragmented(WithDefinedIdSerializer.new(@author))
+          test_id(FragmentedSerializer, 'special_id')
+        end
+
+        private
+
+        def test_type_inflection(serializer_class, expected_type, inflection)
+          original_inflection = ActiveModelSerializers.config.jsonapi_resource_type
+          ActiveModelSerializers.config.jsonapi_resource_type = inflection
+          test_type(serializer_class, expected_type)
+        ensure
+          ActiveModelSerializers.config.jsonapi_resource_type = original_inflection
+        end
+
+        def test_type(serializer_class, expected_type)
+          serializer = serializer_class.new(@model)
+          resource_identifier = ResourceIdentifier.new(serializer)
+          expected = {
+            id: @model.id.to_s,
+            type: expected_type
+          }
+
+          assert_equal(expected, resource_identifier.as_json)
+        end
+
+        def test_id(serializer_class, id)
+          serializer = serializer_class.new(@model)
+          resource_identifier = ResourceIdentifier.new(serializer)
+          inflection = ActiveModelSerializers.config.jsonapi_resource_type
+          type = @model.class.model_name.send(inflection)
+          expected = {
+            id: id,
+            type: type
+          }
+
+          assert_equal(expected, resource_identifier.as_json)
+        end
+      end
+    end
+  end
+end