Add symbol support for ActiveModel::Serializer.type method

The ActiveModel::Serializer.type method now accepts symbol as paremeter:
class AuthorSerializer < ActiveModel::Serializer
  type :profile
end
The test file for the type was also refactored.

CHANGELOG.md

@@ -3,6 +3,8 @@
 Breaking changes:
 
 Features:
+- [#1515](https://github.com/rails-api/active_model_serializers/pull/1515) Adds support for symbols to the
+  `ActiveModel::Serializer.type` method. (@groyoh)
 - [#1504](https://github.com/rails-api/active_model_serializers/pull/1504) Adds the changes missing from #1454
   and add more tests for resource identifier and relationship objects. Fix association block with link
   returning `data: nil`.(@groyoh)

lib/active_model/serializer/type.rb

@@ -17,7 +17,7 @@ module ClassMethods
         #   class AdminAuthorSerializer < ActiveModel::Serializer
         #     type 'authors'
         def type(type)
-          self._type = type
+          self._type = type ? type.to_s : nil
         end
       end
     end

test/adapter/json_api/type_test.rb

@@ -0,0 +1,61 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    module Adapter
+      class JsonApi
+        class TypeTest < ActiveSupport::TestCase
+          class StringTypeSerializer < ActiveModel::Serializer
+            attributes :name
+            type 'profile'
+          end
+
+          class SymbolTypeSerializer < ActiveModel::Serializer
+            attributes :name
+            type :profile
+          end
+
+          def setup
+            @author = Author.new(id: 1, name: 'Steve K.')
+          end
+
+          def with_jsonapi_resource_type inflection
+            old_inflection = ActiveModelSerializers.config.jsonapi_resource_type
+            ActiveModelSerializers.config.jsonapi_resource_type = inflection
+            yield
+          ensure
+            ActiveModelSerializers.config.jsonapi_resource_type = old_inflection
+          end
+
+          def test_config_plural
+            with_jsonapi_resource_type :plural do
+              assert_type(@author, 'authors')
+            end
+          end
+
+          def test_config_singular
+            with_jsonapi_resource_type :singular do
+              assert_type(@author, 'author')
+            end
+          end
+
+          def test_explicit_string_type_value
+            assert_type(@author, 'profile', serializer: StringTypeSerializer)
+          end
+
+          def test_explicit_symbol_type_value
+            assert_type(@author, 'profile', serializer: SymbolTypeSerializer)
+          end
+
+          private
+
+          def assert_type(resource, expected_type, opts = {})
+            opts = opts.reverse_merge(adapter: :json_api)
+            hash = serializable(resource, opts).serializable_hash
+            assert_equal(expected_type, hash.fetch(:data).fetch(:type))
+          end
+        end
+      end
+    end
+  end
+end