<!DOCTYPE html>
<body>
    <h1>frame2</h1>
</body>

<script type="text/javascript">
function test0() {
    let ro = new ResizeObserver(entries => {
        for (let entry of entries) {
            if (entry.target.parentNode) {
                entry.target.parentNode.removeChild(entry.target);
            }
        }
    });
    let frame1 = parent.document.querySelector('#frame1');
    let frame2 = parent.document.querySelector('#frame2');
    ro.observe(frame1);
    ro.observe(frame2);
}

window.addEventListener('message', function(event) {
    switch(event.data) {
        case 'readyToTest':
            test0();
        break;
    }
});
</script>
</html>