test/web-platform-tests/to-upstream/cssom-view/Element-getBoundingClientRect.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>Element.prototype.getBoundingClientRect</title>
<link rel=help href="https://drafts.csswg.org/cssom-view/#dom-element-getboundingclientrect">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<script>
"use strict";

test(() => {

  const zeroDimensions = {
    x: 0,
    y: 0,
    bottom: 0,
    height: 0,
    left: 0,
    right: 0,
    top: 0,
    width: 0
  };

  const el = document.createElement("p");
  assert_object_equals(el.getBoundingClientRect(), zeroDimensions);

}, "getBoundingClientRect should return 0 value dimensions for an element with no associated CSS layout box");
</script>