test: show melange.emit error with dialects

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

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

@@ -0,0 +1,37 @@
+Show missing dependency in Melange when sandboxing is enabled
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.11)
+  > (using melange 0.1)
+  > (dialect
+  >  (name myd)
+  >  (implementation
+  >   (preprocess (run cat %{input-file}))
+  >   (extension myd)))
+  > EOF
+  $ cat > dune <<EOF
+  > (melange.emit
+  >  (target output)
+  >  (alias mel)
+  >  (libraries foo)
+  >  (emit_stdlib false))
+  > EOF
+  $ mkdir lib
+  $ cat > lib/dune <<EOF
+  > (library
+  >  (name foo)
+  >  (modes melange))
+  > EOF
+  $ cat > lib/foo.myd <<EOF
+  > let name = Bar.name
+  > EOF
+  $ cat > lib/bar.ml <<EOF
+  > let name = "Zoe"
+  > EOF
+  $ dune build @mel
+  Error: ocamldep returned unexpected output for _build/default/lib/foo.myd:
+  > lib/foo.myd.ml: Bar
+  -> required by _build/default/output/lib/foo.js
+  -> required by alias mel
+  [1]
+