css/cssom/invalid-pseudo-elements.html

<!doctype html>
<meta charset="utf-8">
<title>CSSOM: Test that rules with invalid pseudo elements are not found</title>
<link rel="author" title="Tim Nguyen" href="https://github.com/nt1m">
<link rel="help" href="https://drafts.csswg.org/cssom/">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
    ::part {}
    ::slotted {}
    ::highlight {}
</style>
<script>
    test(() => {
        assert_equals(document.styleSheets[0].cssRules[0]?.selectorText, undefined, "No associated selectorText");
        assert_equals(document.styleSheets[0].cssRules[0], undefined, "No invalid pseudo element rule should be found");
    });
</script>