chromium/third_party/blink/web_tests/editing/spelling/spelling-linebreak.html

<!doctype html>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script src="../assert_selection.js"></script>
<script src="spellcheck_test.js"></script>

<script>
spellcheck_test(
    '<div contenteditable>Hello,zz a |a</div>',
    '',
    '<div contenteditable>Hello,#zz# a a</div>',
    {
      title: 'Has marker on initially misspelled word',
      callback: sample => spellcheck_test(
          sample,
          'insertLineBreak',
          '<div contenteditable>Hello,#zz# a <br>a</div>',
          'Markers are preserved after adding line break')
    });
</script>