src/third_party/web_platform_tests/html/browsers/history/the-location-interface/reload_post_1-1.html

<script>
onload = function() {opener.next()}
document.write(Math.random());
</script>

<form method="POST" action="">
<input type=hidden name=test value=test>
<input type=submit>
</form>
<button onclick="location.reload()">Reload</button>