New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

services.my-service.js

import Ember from 'ember';

const { RSVP } = Ember;

export default Ember.Service.extend({
  worker: Ember.Object.extend({
    execute() {
      return new RSVP.resolve()
    }
  }),
  
  currentWorker: null,
  
  doWork() {
    // THIS PATH WORKS FINE
  	/*return this.set('currentWorker', this.get('worker').create()).execute().finally(() => {
      this.set('currentWorker', null);
    });*/
    
    // THIS DOES NOT
    
    /*return this.set('currentWorker', this.get('worker').create()).execute().then(() => {
    	// ADDING then there, will result could not call set on destroyed object
      console.log("This is called last")
    }).finally(() => {
      console.log("this is called first");
      this.set('currentWorker', null);
    });*/
    
    // Wrapping it in another Promise with runloop works
    return new RSVP.Promise((resolve, reject) => { this.set('currentWorker', this.get('worker').create()).execute().then(() => {
    	// ADDING then there, will result could not call set on destroyed object
      console.log("This is called first")
      Ember.run(null, resolve);
    })                                                }).finally(() => {
      console.log("this is called last");
      this.set('currentWorker', null);
    });
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

tests.helpers.resolver.js

import Resolver from '../../resolver';
import config from '../../config/environment';

const resolver = Resolver.create();

resolver.namespace = {
  modulePrefix: config.modulePrefix,
  podModulePrefix: config.podModulePrefix
};

export default resolver;

tests.test-helper.js

import resolver from './helpers/resolver';
import {
  setResolver
} from 'ember-qunit';

setResolver(resolver);

tests.unit.services.my-service-test.js

import { moduleFor, test } from 'ember-qunit';

moduleFor('service:my-service', 'TODO: put something here', {
  // Specify the other units that are required for this test.
  // needs: ['service:foo']
});

test('it should do work', function(assert) {
  let service = this.subject();
  service.doWork().then(() => {
    assert.ok('it should get here');
  });
});

twiddle.json

{
  "version": "0.8.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": true
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.5.1",
    "ember-data": "2.5.2",
    "ember-template-compiler": "2.5.1"
  }
}