LayoutTests/fast/loader/resources/early-load-cancel-inner.html

<a id="test" onmousedown="test()">click here</a>
<div id="outer">
</div>
<script>
function test()
{
    document.getElementById("outer").innerHTML = "<iframe src='other.html'></iframe>";
    document.getElementById("outer").innerHTML = "PASSED";
}

onload = async () => {
    testRunner?.waitUntilDone();
    await eventSender?.asyncMouseMoveTo(20, 20);
    await eventSender?.asyncMouseDown();
    testRunner?.notifyDone();
}
</script>