Use mirage config file for both addon and base app in ember-cli-mirage 0.2.*

I am upgrading our desktop and mobile ember apps to mirage (ember-cli-mirage) 0.2.3, from an 0.1.* version. These two apps share a common addon which has a number of test helpers, including a mirage config.

In mirage 0.1.*, the config functions (e.g. the contents of app/mirage/config.js and addon/mirage/config.js, respectively) for both the base app and the addon were executed. In mirage 0.2.3, only the config function for the addon is used; the base app's config is apparently not detected.

Does anyone know how to tell mirage to use both config files?