chromium/third_party/blink/web_tests/accessibility/selection-dom-events.html

<!DOCTYPE html>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>

<p id="para">This is a test</p>

<script>
    test(() =>
    {
        let para = document.getElementById('para');
        let selectstartCount = 0;
        para.addEventListener('selectstart', (e) => {
            selectstartCount++;
            if (selectstartCount === 1)
                e.preventDefault();
        }, true);

        let axPara = accessibilityController.accessibleElementById('para');
        assert_false(axPara.setSelection(axPara, 0, axPara, 1));
        assert_true(axPara.setSelection(axPara, 0, axPara, 1));
    }, 'Test that setting the selection via the accessibility API can be canceled by JavaScript running on the page.');
</script>