position-update-on-font-size-change.html

<!DOCTYPE html>
  <script src="../../resources/ahem.js"></script>
  <script src="../../resources/run-after-layout-and-paint.js"></script>
  <svg>
    <text font-family="Ahem" font-size="10" fill="green"><tspan dy="0.8em">X</tspan></text>
  </svg>
  <script>
    runAfterLayoutAndPaint(_ => {
       document.querySelector('text').setAttribute('font-size', 100);
    }, true);
  </script>

chromium/third_party/blink/web_tests/svg/text/position-update-on-font-size-change.html