Mirage issue with associations

controllers.application.js

import Ember from 'ember';

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

mirage.config.js

export default function() {
  //window.server = this;
  this.get('users/:id');
};

mirage.factories.child.js

import { Factory, faker, association } from 'ember-cli-mirage';

export default Factory.extend({
  name() {
    return faker.name.firstName();
  },
  
  mother: association(),

});

mirage.factories.mother.js

import { Factory, faker, association } from 'ember-cli-mirage';

export default Factory.extend({
  name() {
    return faker.name.firstName();
  },
});

mirage.factories.user.js

import { Factory, faker } from 'ember-cli-mirage';

export default Factory.extend({
  name() {
    return faker.name.findName();
  }

});

mirage.models.user.js

import { Model } from 'ember-cli-mirage';

export default Model.extend({
});

mirage.scenarios.default.js

export default function(server) {
  // added this line because global wasn't created otherwise.
  window.server = server;
  server.create('user');
  
  function logMothers() {
    const numMothers = server.db.mothers.length
    console.log(`We should have 1 mother. Actual number: ${numMothers}`)
  }
  
  const mother = server.create('mother');
  logMothers();
  const child1 = server.create('child', {mother});
  logMothers();
  const child2 = server.create('child', {mother});
  logMothers();
  
  console.log('Mother\'s children (by ID): ' + mother.childIds.join(', '))
  
}

mirage.serializers.application.js

import { JSONAPISerializer } from 'ember-cli-mirage';

export default JSONAPISerializer.extend({
});

models.child.js

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

export default Model.extend({
  mother: belongsTo('mother'),
});

models.mother.js

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

export default Model.extend({
  children: hasMany('children'),
});

models.user.js

import DS from 'ember-data';

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

routes.application.js

import Ember from 'ember';

export default Ember.Route.extend({
  
  model() {
    return this.store.findRecord('user', 1);
  }
  
  
});

routes.index.js

import Ember from 'ember';

export default Ember.Route.extend({
  
  model() {
    return this.store.findRecord('user', 1);
  }
  
  
});

styles.app.css

body {
  margin: 0;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

h1 {
  font-size: 12px;
  font-weight: bold;
  text-align: center;
  text-shadow: none;
  background: #2e4068;
  color: white;
  padding: 20px;
  margin: 0;
  text-transform: uppercase;
}

p {
  font-weight: normal;
}

.pa4 {
  padding: 20px;
}

templates.application.hbs

<h1>Mirage boilerplate</h1>

<div class='pa4'>
  <p>Welcome <strong>{{model.name}}</strong>!</p>
</div>

tests.acceptance.my-acceptance-test.js

import { test } from 'qunit';
import moduleForAcceptance from '../../tests/helpers/module-for-acceptance';

moduleForAcceptance('Acceptance | Users');

test('I can see the users', function(assert) {
  server.create('user', { name: 'Link' });
  
  //visit('/');

  andThen(function() {
    assert.ok(true);
    //assert.ok(find(':contains(Welcome Link!)').length);
  });
});

tests.helpers.destroy-app.js

import Ember from 'ember';

export default function destroyApp(application) {
  Ember.run(application, 'destroy');
}

tests.helpers.module-for-acceptance.js

import { module } from 'qunit';
import startApp from '../helpers/start-app';
import destroyApp from '../helpers/destroy-app';

export default function(name, options = {}) {
  module(name, {
    beforeEach() {
      this.application = startApp();

      if (options.beforeEach) {
        options.beforeEach.apply(this, arguments);
      }
    },

    afterEach() {
      if (options.afterEach) {
        options.afterEach.apply(this, arguments);
      }

      destroyApp(this.application);
    }
  });
}

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.helpers.start-app.js

import Ember from 'ember';
import Application from '../../app';
import config from '../../config/environment';

export default function startApp(attrs) {
  let application;

  let attributes = Ember.merge({rootElement: "#test-root"}, config.APP);
  attributes = Ember.merge(attributes, attrs); // use defaults, but you can override;

  Ember.run(() => {
    application = Application.create(attributes);
    application.setupForTesting();
    application.injectTestHelpers();
  });

  return application;
}

tests.test-helper.js

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

setResolver(resolver);

twiddle.json

{
  "version": "0.13.0",
  "ENV": {
    "ember-cli-mirage": {
    	"enabled": true
		}
	},
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"
  },
  "addons": {
    "ember-data": "2.16.3",
    "ember-cli-mirage": "0.4.2"
  }
}