New Twiddle

controllers.application.js

import Controller from '@ember/controller';
import { inject as service } from '@ember/service';

export default Controller.extend({
  myService: service(),
  appName: 'Ember Twiddle',
  actions: {
    handleClick() {
      this.set('value', this.get('myService').getUrl());
    }
  }
});

services.my-service.js

import Service, { inject as service } from '@ember/service';

export default Service.extend({
  router: service(),
  getUrl() {
    debugger;
    
    return this.router.urlFor('index');
  }
});

templates.application.hbs

<h1>{{this.value}}</h1>
<button {{action 'handleClick'}}>Click Me</button>

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';
import { start } from 'ember-cli-qunit';

setResolver(resolver);
start();

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

import { module, test } from 'qunit';
import { setupTest } from 'ember-qunit';
import Service from '@ember/service';

module('my-service', function(hooks) {
  setupTest(hooks);
  
  test('it exists', function(assert) {
    debugger;
    this.owner.register('service:router', Service.extend({
      urlFor() {
        return 'hello';
      },
    }));
    let service = this.owner.lookup('service:my-service');
    assert.equal(service.getUrl(), 'hello');
  });
});

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": true
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0"
  }
}