How to test Ember error substate, with Ember CLI test runner? - ember.js

Question

I've set up an error substate route/controller/template according to http://guides.emberjs.com/v2.2.0/routing/loading-and-error-substates/. Manually browsing my app, I can trigger error conditions and get directed to the substate. Confirmed with Ember Inspector.
I'd like to automatically test the substate. However, Ember CLI's test runner fails any test when a route's model hook rejects. In other words, the test fails before I can navigate to the error substate.
How can I automatically test my error substate?
Ember: 2.2.0
Ember CLI: 1.13.13

Answer 1

Unfortunately it doesn't seem to be easy to do this in a clean manner.
In its internal tests, Ember uses bootApplication to the route which errors (see github) and is able to directly catch the error. Unfortunately if you try and do any form of try/catch or then/catch around a call to visit in your tests you will find it fails.
When you visit a link which results in an error substate from your acceptance test then Ember's defaultActionHandlers.error gets fired. By design it is not meant to be overridable. It calls logError which calls Ember.default.Logger.error.
So to test this substate we need to temporarily overwrite that method. We can also peek inside the ember container to access the currentRouteName like so (using sinon for the spying):
test('when there is an API error an error message is shown', function(assert) {
const emberLoggerError = Ember.Logger.error;
Ember.Logger.error = sinon.spy();
visit('/users/');
andThen(() => {
// This could be nicer and less private with `getOwner`
let { currentRouteName } = this.application.__container__.lookup('router:main');
assert.equal(currentRouteName, 'users.index_error', 'The current route name is correct');
assert.equal(Ember.Logger.error.callCount, 1, 'The error logger was called');
// Restore the Ember.Logger
Ember.Logger.error = emberLoggerError;
});
});
Things can get even more complicated though. If your visit happens inside a Promise (it did in our case because we were using ember-page-object for our tests) then you have more to deal with...
In a separate loop onerrorDefault of RSVP is triggered which calls Test.adapter.exception AND Ember.default.Logger.error (again!) - passing the stack. So in this case you need to stub and spy on Test.adapter.exception and expect Ember.default.Logger.error to have been called twice!