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chromium/third_party/blink/web_tests/external/wpt/intersection-observer/scroll-and-root-margin.html 

<!DOCTYPE html>
<meta name="viewport" content="width=device-width,initial-scale=1">
<link rel="help" href="https://www.w3.org/TR/intersection-observer/#dom-intersectionobserver-scrollmargin">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="./resources/intersection-observer-test-utils.js"></script>

<style>
#spacer { width: 50px; height: calc(100vh + 10px); }
#target { width: 50px; height: 50px; background-color: green; }
</style>

<div id=spacer></div>
<div id=target></div>

<script>
let entries = [];

window.onload = function() {
  runTestCycle(testIntersection, "Test scroll margin intersection");

  const observer = new IntersectionObserver(
    es => entries = entries.concat(es),
    {
      scrollMargin: "10px",
      rootMargin: "10px"
    }
  );
  observer.observe(target);
};

function testIntersection() {
  assert_equals(entries.length, 1, "IntersectionObserverEntryCount");
  assert_true(entries[0].isIntersecting, "isIntersecting");
  assert_approx_equals(entries[0].intersectionRatio, 0.04, 0.0001, "intersectionRatio");
}
</script>