emberjs tests not running

My tests are not running anymore, abort with this error:

Error: No tests were run.
    at ProcessingQueue.done (webpack://__ember_auto_import__/./node_modules/qunit/qunit/qunit.js?:819:583)
    at ProcessingQueue.advanceTestQueue (webpack://__ember_auto_import__/./node_modules/qunit/qunit/qunit.js?:802:136)
    at ProcessingQueue.advance (webpack://__ember_auto_import__/./node_modules/qunit/qunit/qunit.js?:795:176)
    at unblockAndAdvanceQueue (webpack://__ember_auto_import__/./node_modules/qunit/qunit/qunit.js?:1198:135)

unfortunately I cannot see more of the error-stack. (could I somehow?)

my test-helper.js is a default:

import Application from '../app';
import config from '../config/environment';
import * as QUnit from 'qunit';
import { setApplication } from '@ember/test-helpers';
import { setup } from 'qunit-dom';
import { start } from 'ember-qunit';

setApplication(Application.create(config.APP));

// setup(QUnit.assert);

start();

that's the only left test that is in tests-folder (generated from ember-cli):

import { module, test } from 'qunit';
import { setupRenderingTest } from 'my-stagedoor/tests/helpers';
import { render } from '@ember/test-helpers';
import { hbs } from 'ember-cli-htmlbars';

module('Integration | Helper | filesize', function (hooks) {
    setupRenderingTest(hooks);

    // TODO: Replace this with your real tests.
    test('it renders', async function (assert) {
        this.set('inputValue', '1234');

        await render(hbs`{{filesize this.inputValue}}`);

        assert.dom(this.element).hasText('1234');
    });
});

Any ideas where I can continue to search for that issue?

Versions: qunit: 2.24.2 ember-qunit: ^5.1.5 ember-cli: ^6.3.0 ember-source: ~4.12.1