Test: events around data ready are fired correcctly

[agjohnson]

The changes in

• Use an AddonsApplication to manage load/reload of all addons #504

introduced a bug with data ready event handling. There was a errant return that caused the data ready events to not fire, which was fixed in #544. I was surprised that there were no tests that caught this bug, so it seems we need to test that both the internal and external data ready tests are fired correctly.