chromium/third_party/blink/web_tests/editing/style/designmode.html

<!doctype html>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script src="../assert_selection.js"></script>
<script>
// This tests to make sure that rich editing commands like Bold can be performed
// on text in a document in design mode.
selection_test(
    '<div>^abc|</div>',
    selection => {
        selection.document.designMode = 'on';
        selection.document.execCommand('bold');
    },
    '<div><b>^abc|</b></div>');
</script>