This test passes even if `textToSpeech.stop()` is commented out in Speakerbox.java. Successfully testing this functionality will require adding an implementation for `stop()` to ShadowTextToSpeech.java.

https://github.com/mapzen/speakerbox/blob/master/speakerbox/src/test/java/com/mapzen/speakerbox/ShadowTextToSpeech.java