fix(build): ember-auto-import@2 compatibility

vendor/ember-qunit-assert-helpers-loader.js

@@ -1,4 +1,21 @@
-/* globals require */
-
-// Loading the file here will install the asserts onto `QUnit.Assert` class.
-require('ember-qunit-assert-helpers/test-support/install-qunit-asserts');
+// This file is appended to `test-support.js`.
+// It automatically requires the `install-qunit-asserts` entrypoint module to
+// install the assertions onto `Qunit`.
+//
+// With `ember-auto-import@1` all vanilla JS dependencies, like `qunit`, are
+// eagerly bundled into either `vendor.js` or `test-support.js`.
+// Therefore they are available, when this module is evaluated.
+//
+// With `ember-auto-import@2` these dependencies are placed into extra
+// `*.chunk.js` files instead. These files are loaded _after_ `vendor.js` and
+// `test-support.js`. Therefore they are not available, when this module is
+// evaluated.
+// To fix this, we delay the evaluation of the entry point until the
+// `DOMContentLoaded` event occurs, by which all `<script>` tags will have been
+// loaded.
+//
+// This is not an ideal solution, but only a temporary fix with minimal changes
+// to make this addon work with `ember-auto-import@2` host apps.
+document.addEventListener('DOMContentLoaded', () => {
+  require('ember-qunit-assert-helpers/test-support/install-qunit-asserts');
+});