Disable all observers in your test suite by default. They should not be complicating your model tests because they should have separate concerns anyway. You don't need to unit test that observers actually fire, because ActiveRecord's test suite does that, and your integration tests will cover it.

By using deploy keys, you don’t have to set up a fake user account.

The reason why we don't just create a real DOM tree is that creating DOM nodes and reading the node properties is an expensive operation which is what we are trying to avoid.