ActiveJob is a module

Rakefile

@@ -2,7 +2,6 @@ require 'bundler'
 Bundler::GemHelper.install_tasks
 
 require 'rspec/core/rake_task'
-
 RSpec::Core::RakeTask.new('spec')
 
 task default: :spec

lib/periodicity/extensions/active_job.rb

@@ -1,7 +1,7 @@
 module Periodicity
   module Extensions
-    class ActiveJob
-      def self.perform_every(period, *args)
+    module ActiveJob
+      def perform_every(period, *args)
         @period = Period.new(period, *args)
       end
     end