mozilla-release/testing/web-platform/tests/intersection-observer/inline-with-block-child-client-rect.html

<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="./resources/intersection-observer-test-utils.js"></script>

<style>
pre, #log {
  position: absolute;
  top: 120px;
  left: 0;
}
#target {
  display: inline;
}
</style>

<div id="target">
  <div>
    <img width=100 height=100 />
  </div>
</div>

<script>
var vw = document.documentElement.clientWidth;
var vh = document.documentElement.clientHeight;
var entries = [];
var target;

runTestCycle(function() {
  target = document.getElementById("target");
  assert_true(!!target, "target exists");
  var observer = new IntersectionObserver(function(changes) {
    entries = entries.concat(changes)
  });
  observer.observe(target);
  entries = entries.concat(observer.takeRecords());
  assert_equals(entries.length, 0, "No initial notifications.");
  runTestCycle(step0, "First rAF");
}, "Inline target containing a block child");

function step0() {
  assert_equals(entries.length, 1);
  checkRect(entries[0].boundingClientRect, clientBounds(target),
            "entry.boundingClientRect == target.getBoundingClientRect()");
}
</script>