How to use ember-cli-mirage in an addon project

I can't seem to get ember-cli-mirage to intercept ember-data requests when running ember test --server in an ember-cli-addon project.

/tests/dummy/app/adapters/application.js

export default DS.RESTAdapter.extend({
  namespace: 'rest'
});

/tests/dummy/mirage/config.js

export default function() {

  this.namespace = '/rest';

  this.get('/subManagers', 'sub-manager');
  this.get('/subManagers/:id', 'sub-manager');
  this.post('/subManagers', 'sub-manager');
  this.put('/subManagers/:id', 'sub-manager');
  this.del('/subManagers/:id', 'sub-manager');
}

However, when runnning ember test --server, the following request is getting a 404 http://localhost:7357/rest/subManagers when my test is requesting all subManagers. This is visible in the Chrome console.

The tests are running on http://localhost:7357/6263/tests/index.html?hidepassed

What am I doing wrong?