chromium/third_party/blink/web_tests/editing/spelling/spelling-insert-newline-between-multi-word-misspelling.html

<!doctype html>
<meta charset="utf-8"/>
<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>It should be upper |case.</div>',
    '',
    '<div contenteditable>It should be #upper case#.</div>',
    {
      title: 'Has marker on initial multi-word misspelling.',
      callback: sample => spellcheck_test(
          sample,
          document => document.execCommand('insertText', false, '\n'),
          '<div contenteditable>It should be upperĀ <div>case.</div></div>',
          'Marker disappears after inserting newline in multi-word misspelling.')
    });
</script>