s/an/a/

railties/test/application/middleware/exceptions_test.rb

@@ -102,7 +102,7 @@ def index
       end
     end
 
-    test "routing to an nonexistent controller when action_dispatch.show_exceptions and consider_all_requests_local are set shows diagnostics" do
+    test "routing to a nonexistent controller when action_dispatch.show_exceptions and consider_all_requests_local are set shows diagnostics" do
       app_file "config/routes.rb", <<-RUBY
         Rails.application.routes.draw do
           resources :articles