Expose a simple Queue#wait to block until all notifications are drained

activesupport/lib/active_support/notifications.rb

@@ -154,10 +154,15 @@ def subscribe(pattern=nil, &block)
         @listeners << Listener.new(pattern, &block)
       end
 
-      def drained?
-        @listeners.all? &:drained?
+      def wait
+        sleep 0.05 until drained?
       end
 
+      private
+        def drained?
+          @listeners.all? &:drained?
+        end
+
       class Listener
         def initialize(pattern, &block)
           @pattern = pattern

activesupport/test/notifications_test.rb

@@ -201,6 +201,6 @@ def test_with_several_consumers_and_several_events
 
   private
     def drain
-      sleep(0.1) until ActiveSupport::Notifications.queue.drained?
+      ActiveSupport::Notifications.queue.wait
     end
 end