LayoutTests/fast/css/insertrule-namespace-after-layer.html

<style>
    @layer x;
</style>
<script>
if(window.testRunner)
  testRunner.dumpAsText();

onload = () => {
  console.log(document.styleSheets[0].insertRule(`@namespace url();`, 1));
};
</script>
Test passes if doesn't crash