quals(parent.childNodes, []);
    }, nodeName + '.append() without any argument, on a parent having no child.');

    test(function() {
        const parent = node.cloneNode();
        parent.append(null);
        assert_equals(parent.childNodes[0].textContent, 'null');
    }, nodeName + '.append() with null as an argument, on a parent having no child.');

    test(function() {
        const parent = node.cloneNode();
        parent.append(undefined);
        assert_equals(parent.childNodes[0].textContent, 