My answer to "How to test Ember error substate, with Ember CLI test runner?" http://stackoverflow.com/q/34074386/62269

override-test-adapter-exception-test.js

import Ember from 'ember';
import moduleForAcceptance from '../helpers/module-for-acceptance';
import sinon from 'sinon';

const { Test } = Ember;

moduleForAcceptance('Acceptance | error', {
  beforeEach() {
    this.sandbox = sinon.sandbox.create();

    // Override Ember.Test's default failure on uncaught errors. See http://stackoverflow.com/a/34138273/62269
    this.sandbox.stub(Test.adapter, 'exception');
  },

  afterEach() {
    this.sandbox.restore();
  }
});