How does ember test discover tests for in-repo-addons?

TL;DR Is anyone successfully running unit tests from within an in-repo-addon?

I saw a related post (ember-cli run tests from in-repo addons) that mentioned that it is possible to write tests in a "test-support" folder within the in-repo-addon. I tried this, and the tests are not being found when running ember test. Is there something else required to be able to discover these tests? Or perhaps something has changed since the post?