How to create ember-cli addon for test helpers?

I've had some good luck sharing production code with ember-cli but how can I create an addon to share test helper functions/objects?

The addon already has a "tests" folder but I assume it's used to run the unit/acceptance tests for the addon itself. Can you/should you put code into the helpers and "npm install" it just to use those helpers?

Or ... should you instead put the "helper" code inside the addon/tests/helpers folder?