Double willDestroy

controllers.application\.js

import Controller from '@ember/controller';

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

helpers.my-helper\.js

import Helper from '@ember/component/helper';

class FullStackError extends Error {
  constructor() {
    let limit = Error.stackTraceLimit;
    Error.stackTraceLimit = Infinity;
    try {
      super(...arguments);
    } finally {
      Error.stackTraceLimit = limit;
    }
  }
}

export default class MyHelper extends Helper {
  compute() {
  }

  willDestroy() {
    if (this.willDestroyStack) {
      throw new Error(`willDestroy() called twice\n\nfirst call:\n\n ${this.willDestroyStack.stack}\n\nsecond call:\n\n${new FullStackError().stack}`);
    } else {
      this.willDestroyStack = new FullStackError();
    }
    super.willDestroy(...arguments);
  }
}

templates.application\.hbs

<h1>Welcome to {{this.appName}}</h1>
<br>
<br>
{{my-helper}}
<br>
<br>

tests.acceptance.my-acceptance-test\.js

import { module, test } from 'qunit';
import { visit, currentURL } from '@ember/test-helpers';
import { setupApplicationTest } from 'ember-qunit';

module('double willDestroy', function(hooks) {
  setupApplicationTest(hooks);

  test('visiting /my-acceptance', async function(assert) {
    assert.expect(0);
    await visit('/');
  });
});

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": "0.17.0",
  "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/3.3.1/jquery.js",
    "ember": "3.17.0",
    "ember-template-compiler": "3.17.0",
    "ember-testing": "3.17.0"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}