Dont need the explicit error handling -- if the require fails, it will raise exactly the error we want to communicate anyway. Also use the load path, so we can allow plugins, rather than requre_relative

lib/active_job/base.rb

@@ -1,9 +1,7 @@
-require 'active_job/errors'
 require 'active_job/queue_adapters/inline_adapter'
 require 'active_support/core_ext/string/inflections'
 
 module ActiveJob
-
   class Base
     cattr_accessor(:queue_adapter)   { ActiveJob::QueueAdapters::InlineAdapter }
     cattr_accessor(:queue_base_name) { "active_jobs" }
@@ -19,19 +17,9 @@ module ActiveJob
       end
 
       def adapter=(adapter_name)
-        adapter_name = adapter_name.to_s
+        require "active_job/queue_adapters/#{adapter_name}_adapter"
-        unless %w(inline resque sidekiq sucker_punch).include?(adapter_name)
+        ActiveJob::Base.queue_adapter = "ActiveJob::QueueAdapters::#{adapter_name.to_s.camelize}Adapter".constantize
-          fail ActiveJob::NotImplementedError
-        end
-
-        begin
-          require_relative "queue_adapters/#{adapter_name}_adapter"
-          ActiveJob::Base.queue_adapter = "ActiveJob::QueueAdapters::#{adapter_name.camelize}Adapter".constantize
-        rescue
-          fail ActiveJob::Error.new("#{adapter_name} is missing")
       end
     end
   end
-
-  end
 end

lib/active_job/errors.rb

@@ -1,12 +0,0 @@
-module ActiveJob
-
-  class NotImplementedError < ::NotImplementedError #:nodoc:
-  end
-
-  class Error < ::StandardError #:nodoc:
-    def initialize(message = nil)
-      super(message)
-    end
-  end
-
-end