[devtools] use self._parse so AssertionError is properly raised instead of lxml error (test failure introduced in 6711f78c18be)
<html>
<head>
<!-- dependencies -->
<script type="text/javascript" src="../../data/jquery.js"></script>
<script src="../../data/cubicweb.python.js" type="text/javascript"></script>
<script src="../../data/cubicweb.js" type="text/javascript"></script>
<script src="../../data/cubicweb.compat.js" type="text/javascript"></script>
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<body>
<div id="main"> </div>
<h1 id="qunit-header">cubicweb.htmlhelpers.js functions tests</h1>
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