chromium/third_party/blink/web_tests/editing/execCommand/19403.html

<div id="description">This tests for an ASSERT during a RemoveFormat call when it's called on a selection containing only a horizontal rule.  It should not ASSERT.</div>
<div id="edit" contentEditable="true"><hr></div>

<script>
if (window.testRunner)
    testRunner.dumpAsText();
edit = document.getElementById("edit");
edit.focus();
document.execCommand("SelectAll");
document.execCommand("RemoveFormat");
if (window.testRunner)
    document.body.innerText = document.getElementById("description").innerText + "\n" + edit.innerHTML;
</script>