<NME> config.ru
<BEF> ADDFILE
<MSG> Test rackup file

<DFF> @@ -0,0 +1,5 @@
+# encoding: utf-8
+
+use Rack::ContentType
+use Rack::ContentLength
+run lambda { |env| [200, Hash.new, "Just a test!"] }

Test rackup file