At least one use of QUnit.asyncTest found in MobileFrontend (deprecated since QUnit 1.16, removed in QUnit 2). Core currently uses QUnit 1.23.
$ git grep asyncTest tests/qunit/mobile.search.api/test_SearchGateway.js: QUnit.asyncTest( 'Wikidata Description in search results', 3, function ( assert ) {
Migrate to either returning a Promise to QUnit.test(), or use assert.async().
https://api.qunitjs.com/QUnit/test
https://api.qunitjs.com/assert/async