ED test failure

adapters.application.js

import RESTAdapter from 'ember-data/adapters/rest';

export default RESTAdapter.extend();

models.bar.js

import Model from 'ember-data/model';
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';

export default Model.extend({
  name: attr('string')
});

models.foo.js

import Model from 'ember-data/model';
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';

export default Model.extend({
  name: attr('string'),
  bar: belongsTo('bar')
});

routes.my-route.js

import Ember from 'ember';

export default Ember.Route.extend({
});

serializers.application.js

import RESTSerializer from 'ember-data/serializers/rest';

export default RESTSerializer.extend();

templates.application.hbs

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

tests.test-helper.js

import Application from '../app';
import config from '../config/environment';
import { setApplication } from '@ember/test-helpers';
import { start } from 'ember-qunit';
import { assign } from '@ember/polyfills';

let attributes = assign({ rootElement: '#main' }, config.APP);
setApplication(Application.create(attributes));

start();

tests.unit.routes.my-route-test.js

import { moduleFor, test } from 'ember-qunit';
import Ember from 'ember';
const { getOwner, run } = Ember;

moduleFor('route:my-route', {
  needs: [
    'adapter:application',
    'serializer:application',
    'model:foo',
    'model:bar'
  ] 
});

test('rels', function(assert) {
  const owner = getOwner(this);
  const store = owner.lookup('service:store');
  const adapter = owner.lookup('adapter:application');
  
  store.pushPayload({
    foos: [{
      id: '1',
      name: 'Foo 1',
      bar: '1'
    }],
    bars: [{
      id: '1',
      name: 'Bar 1'
    }, {
      id: '2',
      name: 'Bar 2'
    }]
  });
  
  const foo = store.peekRecord('foo', 1);
  const bar = store.peekRecord('bar', 1);
  
  run(() => {
    foo.belongsTo('bar').push({
      data: {
        type: 'bar',
        id: '2'
      }
    });
  });
  
  foo.get('bar').then(fooBar => {
    assert.deepEqual(fooBar.serialize(), {
      name: 'Bar 2'
    });
  });
  
  
});

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": true
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}