Add spec for proc methods with optional arguments

spec/lib/object_serializer_class_methods_spec.rb

@@ -235,6 +235,7 @@ describe FastJsonapi::ObjectSerializer do
       before do
         movie.release_year = 2008
         MovieSerializer.attribute :released_in_year, &:release_year
+        MovieSerializer.attribute :name, &:local_name
       end
 
       after do
@@ -242,7 +243,7 @@ describe FastJsonapi::ObjectSerializer do
       end
 
       it 'returns correct hash when serializable_hash is called' do
-        expect(serializable_hash[:data][:attributes][:name]).to eq movie.name
+        expect(serializable_hash[:data][:attributes][:name]).to eq "english #{movie.name}"
         expect(serializable_hash[:data][:attributes][:released_in_year]).to eq movie.release_year
       end
     end

spec/shared/contexts/movie_context.rb

@@ -54,6 +54,10 @@ RSpec.shared_context 'movie class' do
         "#{id}"
       end
 
+      def local_name(locale = :english)
+        "#{locale} #{name}"
+      end
+
       def url
         "http://movies.com/#{id}"
       end