test: demonstrate the same issue if preprocessing is added on the

library

Signed-off-by: Antonio Nuno Monteiro <anmonteiro@gmail.com>

test/blackbox-tests/test-cases/melange/unexpected-ocamldep-output.t

@@ -31,3 +31,22 @@ file after any dialects have run
   > EOF
   $ dune build @mel
 
+Now try preprocessing too
+
+  $ dune clean
+  $ cat > lib/dune <<EOF
+  > (library
+  >  (name foo)
+  >  (preprocess (action (run cat %{input-file})))
+  >  (modes melange))
+  > EOF
+  $ dune build @mel
+  Error: ocamldep returned unexpected output for _build/default/lib/bar.ml:
+  > lib/bar.pp.ml:
+  -> required by _build/default/output/lib/bar.js
+  -> required by alias mel
+  Error: ocamldep returned unexpected output for _build/default/lib/foo.myd.ml:
+  > lib/foo.pp.myd.ml: Bar
+  -> required by _build/default/output/lib/foo.js
+  -> required by alias mel
+  [1]