<style>
#target { cursor:url(file:///non-existent.png), auto; }
</style>
<div id=target></div>
<pre id=log></pre>
<script>
if (window.testRunner)
    testRunner.dumpAsText();

const cursorValue = getComputedStyle(target).getPropertyCSSValue("cursor");

log.innerText = cursorValue.item(0).cssText;
</script>