is there an example of using lambaisland.classpath/update-classpath! to add a new path to the class path?

the reference to deps/create-basis isn't lead to much illustrative documentation or examples

here's what I'm trying rn

(classpath/update-classpath!
     {:extra
      {:extra-paths ["test_runner"]}})

or rather, it does do something because my app totally breaks in a new way after I do that. but it's not reflected when I (println (classpath/classpath-directories))