chore: improve readme

README.md

@@ -239,8 +239,7 @@ In case you need to pass options, you can call the serializer manually:
 
 ```ruby
 class SongSerializer < Oj::Serializer
-  attribute
-  def album
+  attribute :album do
     AlbumSerializer.one(song.album, for_song: song)
   end
 end
@@ -368,7 +367,7 @@ One slight variation that might make it easier to maintain in the long term is
 to use a separate singleton service to provide the url helpers and options, and
 make it available as `urls`.
 
-### Memoization & Local State
+### Memoization & local state
 
 Serializers are designed to be stateless so that an instanced can be reused, but
 sometimes it's convenient to store intermediate calculations.
@@ -404,7 +403,7 @@ class PersonSerializer < Oj::Serializer
 end
 
 PersonSerializer.one('first_name' => 'Mary', :middle_name => 'Jane', :last_name => 'Watson')
-# {"first_name":"Mary","last_name":"Watson"}
+# {first_name: "Mary", last_name: "Watson"}
 ```
 
 ### `mongo_attributes` 🚀

lib/oj_serializers/serializer.rb

@@ -43,7 +43,7 @@ def options
     def _check_instance_variables
       if instance_values.keys.any? { |key| !ALLOWED_INSTANCE_VARIABLES.include?(key) }
         bad_keys = instance_values.keys.reject { |key| ALLOWED_INSTANCE_VARIABLES.include?(key) }
-        raise ArgumentError, "Serializer instances are reused so they must be stateless. Use `memo.fetch` for memoization purposes instead. Bad keys: #{bad_keys.join(',')}"
+        raise ArgumentError, "Serializer instances are reused so they must be stateless. Use `memo.fetch` for memoization purposes instead. Bad keys: #{bad_keys.join(',')} in #{self.class}"
       end
     end
   end
@@ -532,7 +532,7 @@ def code_to_rescue_no_method
     # Internal: Detects any include methods defined in the serializer, or defines
     # one by using the lambda passed in the `if` option, if any.
     def check_conditional_method(method_name, options)
-      include_method_name = "include_#{method_name}#{'?' unless method_name.ends_with?('?')}"
+      include_method_name = "include_#{method_name}#{'?' unless method_name.to_s.ends_with?('?')}"
       if render_if = options[:if]
         if render_if.is_a?(Symbol)
           alias_method(include_method_name, render_if)

spec/oj_serializers/dev_mode_spec.rb

@@ -26,7 +26,7 @@ class MissingAttributeSerializer < Oj::Serializer
 
   it 'should fail early when memoization is used incorrectly' do
     expect { StatefulSerializer.many([album, album]) }
-      .to raise_error(ArgumentError, 'Serializer instances are reused so they must be stateless. Use `memo.fetch` for memoization purposes instead. Bad keys: name')
+      .to raise_error(ArgumentError, 'Serializer instances are reused so they must be stateless. Use `memo.fetch` for memoization purposes instead. Bad keys: name in StatefulSerializer')
   end
 
   it 'should fail early when `attributes` is used instead of `serializer_attributes`' do