message: chore: add TESTS_ENABLED to useful overrides in handbook
diff: @@ -26,6 +26,12 @@ This thing you're reading right now? It's the handbook. If you'd like to be able
  [Mirage](http://www.ember-cli-mirage.com) is a client-side API server that we use to mock the OSF API during automated testing. It can also be used for local development. Setting this to true will allow you to run the OSF front-end without having to run the OSF API back-end.
  +#### TESTS_ENABLED
  +* **Type**: _boolean_
  +* **Default**: false
  +
  +This controls whether tests are included in `development` builds. Set this to `true` if you wish to run tests by accessing `/tests` when you `ember serve`.
  +
  #### A11Y_AUDIT
  * **Type**: _boolean_
  * **Default**: true (well, in develop mode)
  