Extract attributes filtering from serializer into adapter.

test/serializers/fieldset_test.rb

@@ -4,22 +4,11 @@ module ActiveModel
   class Serializer
     class FieldsetTest < Minitest::Test
       def test_fieldset_with_hash
-        fieldset = ActiveModel::Serializer::Fieldset.new({ 'post' => %w(id title), 'coment' => ['body'] })
+        fieldset = ActiveModel::Serializer::Fieldset.new('post' => %w(id title), 'comment' => ['body'])
+        expected = { :post => [:id, :title], :comment => [:body] }
 
-        assert_equal(
-          { :post => [:id, :title], :coment => [:body] },
-          fieldset.fields
-        )
-      end
-
-      def test_fieldset_with_array_of_fields_and_root_name
-        fieldset = ActiveModel::Serializer::Fieldset.new(['title'], 'post')
-
-        assert_equal(
-          { :post => [:title] },
-          fieldset.fields
-        )
+        assert_equal(expected, fieldset.fields)
       end
     end
   end
-end
+end