Restrict serializable_hash to accepted options, only for tests

lib/active_model/serializer.rb

@@ -18,6 +18,8 @@ require 'active_model/serializer/type'
 # reified when subclassed to decorate a resource.
 module ActiveModel
   class Serializer
+    # @see #serializable_hash for more details on these valid keys.
+    SERIALIZABLE_HASH_VALID_KEYS = [:only, :except, :methods, :include, :root].freeze
     extend ActiveSupport::Autoload
     autoload :Adapter
     autoload :Null

lib/active_model_serializers/adapter/attributes.rb

@@ -8,7 +8,7 @@ module ActiveModelSerializers
       end
 
       def serializable_hash(options = nil)
-        options ||= {}
+        options = serialization_options(options)
 
         if serializer.respond_to?(:each)
           serializable_hash_for_collection(options)

lib/active_model_serializers/adapter/base.rb

@@ -19,6 +19,8 @@ module ActiveModelSerializers
         @cached_name ||= self.class.name.demodulize.underscore
       end
 
+      # Subclasses that implement this method must first call
+      #   options = serialization_options(options)
       def serializable_hash(_options = nil)
         fail NotImplementedError, 'This is an abstract method. Should be implemented at the concrete adapter.'
       end
@@ -41,6 +43,12 @@ module ActiveModelSerializers
 
       private
 
+      # see https://github.com/rails-api/active_model_serializers/pull/965
+      # When <tt>options</tt> is +nil+, sets it to +{}+
+      def serialization_options(options)
+        options ||= {} # rubocop:disable Lint/UselessAssignment
+      end
+
       def meta
         instance_options.fetch(:meta, nil)
       end

lib/active_model_serializers/adapter/json.rb

@@ -2,7 +2,7 @@ module ActiveModelSerializers
   module Adapter
     class Json < Base
       def serializable_hash(options = nil)
-        options ||= {}
+        options = serialization_options(options)
         serialized_hash = { root => Attributes.new(serializer, instance_options).serializable_hash(options) }
         self.class.transform_key_casing!(serialized_hash, instance_options)
       end