css/cssom/base-uri.html

<!doctype html>
<meta charset="utf-8">
<title>CSSOM base URI is the document's base URI</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<link rel="author" title="Mozilla" href="https://mozilla.org">
<link rel="help" href="https://html.spec.whatwg.org/#document-base-url">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1343919">
<base href="/non-existent-base/">
<script src='/resources/testharness.js'></script>
<script src='/resources/testharnessreport.js'></script>
<div id="target"></div>
<script>
const target = document.getElementById("target");
const kRelativeURI = "url(something.png)";
const kKeyframes = [
  { backgroundImage: kRelativeURI },
  { backgroundImage: kRelativeURI },
];
function assertBackground() {
  const image = getComputedStyle(target).backgroundImage;
  assert_true(image.includes("non-existent-base"), image);
}
function assertNoBackground() {
  const image = getComputedStyle(target).backgroundImage;
  assert_equals(image, "none");
}

promise_test(async function() {
  target.style.backgroundImage = kRelativeURI;
  assertBackground();
  target.style.backgroundImage = "";
  assertNoBackground();
}, "setProperty");

promise_test(async function() {
  const keyframe = new KeyframeEffect(target, kKeyframes, 10000);
  const animation = new Animation(keyframe, document.timeline);
  animation.play();
  await animation.ready;
  assertBackground();
  animation.cancel();
  assertNoBackground();
}, "KeyframeEffect constructor");

promise_test(async function() {
  const keyframe = new KeyframeEffect(target, [], 10000);
  keyframe.setKeyframes(kKeyframes);
  const animation = new Animation(keyframe, document.timeline);
  animation.play();
  await animation.ready;
  assertBackground();
  animation.cancel();
  assertNoBackground();
}, "KeyframeEffect.setKeyframes");
</script>