Test that a Rails.queue consumer is automatically started in production

railties/lib/rails/application/configuration.rb

@@ -44,7 +44,7 @@ def initialize(*)
         @autoflush_log                 = true
         @log_formatter                 = ActiveSupport::Logger::SimpleFormatter.new
         @queue                         = ActiveSupport::SynchronousQueue.new
-        @queue_consumer                = ActiveSupport::ThreadedQueueConsumer
+        @queue_consumer                = nil
         @eager_load                    = nil
 
         @assets = ActiveSupport::OrderedOptions.new

railties/lib/rails/application/finisher.rb

@@ -98,7 +98,8 @@ module Finisher
 
       initializer :activate_queue_consumer do |app|
         if config.queue.class == ActiveSupport::Queue
-          app.queue_consumer = config.queue_consumer.start
+          app.queue_consumer = config.queue_consumer || config.queue.consumer
+          app.queue_consumer.start
           at_exit { app.queue_consumer.shutdown }
         end
       end

railties/test/application/queue_test.rb

@@ -69,6 +69,17 @@ def ran?
       refute job.ran_in_different_thread?, "Expected job to run in the same thread"
     end
 
+    test "in production, automatically spawn a queue consumer in a background thread" do
+      add_to_env_config "production", <<-RUBY
+        config.queue = ActiveSupport::Queue.new
+      RUBY
+
+      app("production")
+
+      assert_nil Rails.application.config.queue_consumer
+      assert_kind_of ActiveSupport::ThreadedQueueConsumer, Rails.application.queue_consumer
+    end
+
     test "attempting to marshal a queue will raise an exception" do
       app("test")
       assert_raises TypeError do
@@ -123,7 +134,6 @@ class MyQueueConsumer
 
           def start
             @started = true
-            self
           end
         end
       RUBY