chromium/third_party/blink/web_tests/svg/text/text-positioning-mutate-textnode-2.html

<!DOCTYPE html>
<script src="../../resources/run-after-layout-and-paint.js"></script>
<svg>
  <text y="20">
    foo
    <tspan dx="50">baz</tspan>
  </text>
</svg>
<script>
runAfterLayoutAndPaint(function() {
  let text = document.querySelector('tspan').previousSibling;
  text.textContent = text.textContent + "bar";
}, true);
</script>