async-await-shenanigans

components.my-component\.js

import Component from '@glimmer/component';
import { action } from '@ember/object';
import { tracked } from '@glimmer/tracking';

export default class extends Component {
  @tracked foo = undefined;
  @tracked bar = undefined;

  @action
  async clickMe() {
    console.log('start clickMe()');

    this.otherFunction1();
    this.otherFunction2();
    
    console.log('finish clickMe()');
  }

	otherFunction1() {
    this.foo = 'foo';
  }

	async otherFunction2() {
    this.bar = 'bar';
  }
}

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';
}

templates.application\.hbs

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

templates.components.my-component\.hbs

<div data-test-output>
	{{this.foo}}{{this.bar}}
</div>

<button type="button" data-test-button {{on "click" this.clickMe}}>
	Click me
</button>

tests.integration.components.my-component-test\.js

import { module, test } from 'qunit';
import { setupRenderingTest } from 'ember-qunit';
import { click, render } from '@ember/test-helpers';
import hbs from 'htmlbars-inline-precompile';

module('my-component', function(hooks) {
  setupRenderingTest(hooks);

  test('it fails without await', async function(assert) {
    await render(hbs`<MyComponent />`);
    
    console.log('before click');
    await click('[data-test-button]');

    console.log('before assert');
    assert.equal(this.element.querySelector('[data-test-output]').textContent.trim(), 'bar');
  });
  
  test('it does not fail with await', async function(assert) {
    await render(hbs`<MyComponent />`);
 
    console.log('before click');
    await click('[data-test-button]');

    console.log('before assert');
    assert.equal(this.element.querySelector('[data-test-output]').textContent.trim(), 'bar');
  });
});
//

tests.test-helper\.js

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

let attributes = {
  rootElement: '#test-root',
  autoboot: false
};
attributes = assign(attributes, config.APP);

let application = Application.create(attributes);
setApplication(application);

start();

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": true
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}