test(function(t) {
    assert_implements(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
    beforeRender = performance.now();
    const img = document.createElement('img');
    img.src = 'resources/square20.jpg';
    img.setAttribute('elementtiming', 'my_image');
    img.setAttribute('id', 'my_id');
    document.body.appendChild(img);

    // this PerformanceObserver should be notified about the previously
    // buffered element entry
    new PerformanceObserver(t.step_fun