Included testing integration?

Testing always seems to get short shrift in libraries. It would be nice to see an included test helper for simulating file selection, especially since this has become harder (if not impossible) with x-file-input in Ember 2.5+ since you basically have to re-tool the `change` handler to work out the readonly nature of event.target, event.target.files, etc.

Source: [Blog Post](https://medium.com/@chrisdmasters/acceptance-testing-file-uploads-in-ember-2-5-1c9c8dbe5368#.j3bxj7f5h) / [Issue](https://github.com/emberjs/ember.js/issues/13540)