chromium/third_party/blink/web_tests/editing/style/unbold-in-bold.html

<!doctype html>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script src="../assert_selection.js"></script>
<script>
    test(() => assert_selection(
        '<div contenteditable>|</div>',
        selection => {
            selection.document.execCommand('bold');
            selection.document.execCommand('insertText', false, 'abc');
        },
        '<div contenteditable><b>abc|</b></div>'),
        'bold+insertText');

    test(() => assert_selection(
        '<div contenteditable>^abc|</div>',
        'bold',
        '<div contenteditable><b>^abc|</b></div>'),
        'add bold');

    test(() => assert_selection(
        '<div contenteditable><b>^abc def|</b></div>',
        'bold',
        '<div contenteditable>^abc def|</div>'),
        'remove bold fully');

    test(() => assert_selection(
        '<div contenteditable><b>abc ^def| ghi</b></div>',
        'bold',
        '<div contenteditable><b>abc </b>^def|<b> ghi</b></div>'),
        'remove bold partially');
</script>