chromium/src/third_party/blink/web_tests/fast/forms/number/number-spinbutton-increment-decrement-state-expected.html

<input id="num1" type="number" value="0">
<div>input number value: -1</div>
<script>
    var num1 = document.getElementById("num1");
    var mouseX = num1.offsetLeft + num1.offsetWidth - 5;
    var mouseY = num1.offsetTop + 5;
    eventSender.mouseMoveTo(mouseX, mouseY);
    eventSender.mouseDown();
</script>