We need to ensure that the prepare_npm_stuff is always invoked in same shell, because it adjust a number of paths, envs... that the caller needs.
This is because, since https://github.com/moodlehq/moodle-local_ci/pull/210 we are managing everything from that script using nvm.
And we had to, quickly, go for https://github.com/moodlehq/moodle-local_ci/pull/212 because we had some uses calling it via sub-shell.
So this is about to make the prepare_npm_stuff script self-aware and error when not sourced. It seems that can be done: https://stackoverflow.com/a/2684300