access dummy project root from ember cli addon in tests

Scenario: I'd like to know the proper way to access the root of a project that's consuming the addon - that also works while testing...

e.g., the addon:

// ember-cli-myaddon/index.js
{

  ...

  contentFor(name) {
    if (name ==='body') {
      var filePath = path.join(this.app.project.root, 'app/some-file.html')
      var file = fs.readFileSync(filePath);

      return [file];
    }
  },

  ...

}

^ that works when using the addon inside an actual project.

However when I run tests for the addon, this.app.project.root is ~/ember-cli-myaddon/app/some-file.html

When I expect (need) it to be ~/ember-cli-myaddon/tests/dummy/app/some-file.html