LayoutTests/fast/dom/MutationObserver/clear-transient-without-delivery.html

<script src="../../../resources/js-test-pre.js"></script>
<script>
window.jsTestIsAsync = true;
description('Transient registrations should be cleared even without delivery.');

var mutationsDelivered = false;
function callback(mutations) {
    mutationsDelivered = true;
}
var observer = new MutationObserver(callback);

var div = document.createElement('div');
var span = div.appendChild(document.createElement('span'));
observer.observe(div, {attributes: true, subtree: true});
div.removeChild(span);
setTimeout(function() {
    // By the time this function runs the transient registration should be cleared,
    // so we expect not to be notified of this attribute mutation.
    span.setAttribute('bar', 'baz');
    setTimeout(function() {
        shouldBeFalse('mutationsDelivered');
        finishJSTest();
    }, 0);
}, 0);
</script>
<script src="../../../resources/js-test-post.js"></script>