Make -unused-code-warning tests actual tests

test/deriving_warning/ppx/ppx_warning_flags.ml → test/deriving_warning/driver.ml

@@ -93,3 +93,5 @@ let () =
   (* The derivers are added from right to left *)
   Deriving.add_alias "alias_warn" [ alias_no_warn; alias_do_warn ]
   |> Deriving.ignore
+
+let () = Driver.standalone ()

test/deriving_warning/dune

@@ -0,0 +1,8 @@
+(executable
+ (name driver)
+ (libraries ppxlib)
+ (preprocess
+  (pps ppxlib.metaquot)))
+
+(cram
+ (deps driver.exe))