LayoutTests/fast/repaint/text-content-shrinks-repaint.html

<style>
.container {
  display: flex;
  font-size: 20px;
  font-family: Monospace;
}
</style>
<div class=container><div id=inlinebox>not great</div></div>
<script src="../../resources/ui-helper.js"></script>
<script>
if (window.testRunner) {
  testRunner.dumpAsText();
  testRunner.waitUntilDone();
}

async function repaintTest() {
  if (window.internals)
    internals.startTrackingRepaints();

  inlinebox.firstChild.nodeValue = "Pass if this line is properly repainted.";

  await UIHelper.renderingUpdate();
 
  if (window.internals) {
    var repaintRects = internals.repaintRectsAsText();
    internals.stopTrackingRepaints();
    var pre = document.createElement('pre');
    pre.innerText = repaintRects;
    document.body.appendChild(pre);
  }

  if (window.testRunner)
    testRunner.notifyDone();
}
setTimeout(repaintTest, 0);

</script>