These two elements are not being torn down, and also not part of qunit-fixture (in which case teardown would happen automatically). One of those two needs to happen.
<form class="mw-api-upload-form" action="/w/api.php" method="POST" target="uploadframe-0" enctype="multipart/form-data" style="display: none;"> <input type="hidden" name="action" value="upload"> <input type="hidden" name="format" value="json"> <input name="file"> <input type="hidden" name="filename" value="Testing API upload.jpg"> </form> <iframe id="uploadframe-0" name="uploadframe-0" src="about:blank" style="display: none;"></iframe>