(rule
 (deps
  (package mdx)
  (source_tree environment-variable-unset))
 (action
  (with-stdout-to
   test-case.output
   (setenv
    VAR
    val
    (run ocaml-mdx test --output - %{dep:test-case.md})))))

(rule
 (alias runtest)
 (action
  (diff test-case.md test-case.output)))
