chromium/src/third_party/blink/web_tests/http/tests/priority-hints/image-initial-load.html

<script src=../priorities/resources/common.js></script>
<script src=../resources/testharness.js></script>
<script src=../resources/testharnessreport.js></script>

<script>
const priority_tests = [
  {
    promise: internals.getResourcePriority(new URL('../resources/square.png', location), document),
    expected_priority: kHigh,
    description: 'high importance on <img> must translate to kHigh resource load priority'
  },
  {
    promise: internals.getResourcePriority(new URL('../resources/square.png?1', location), document),
    expected_priority: kLow,
    description: 'low importance on <img> must translate to kLow resource load priority'
  },
  {
    promise: internals.getResourcePriority(new URL('../resources/square.png?2', location), document),
    expected_priority: kLow,
    description: 'auto importance on <img> must translate to kLow resource load priority'
  },
  {
    promise: internals.getResourcePriority(new URL('../resources/square.png?3', location), document),
    expected_priority: kLow,
    description: 'invalid importance on <img> must translate to kLow resource load priority'
  },
  {
    promise: internals.getResourcePriority(new URL('../resources/square.png?3', location), document),
    expected_priority: kLow,
    description: 'missing importance on <img> must translate to kLow resource load priority'
  }
];

</script>

<img id=img1 importance=high src=../resources/square.png alt=img>
<img id=img2 importance=low src=../resources/square.png?1 alt=img>
<img id=img3 importance=auto src=../resources/square.png?2 alt=img>
<img id=img4 importance=xyz src=../resources/square.png?3 alt=img>
<img id=img5 src=../resources/square.png?4 alt=img>

<script>
  promise_test(async (t) => {
    await new Promise(resolve => {
      addEventListener('DOMContentLoaded', resolve);
    });

    const base_msg = " was fetched by the preload scanner";
    assert_true(internals.isPreloaded(img1.src), img1.src + base_msg);
    assert_true(internals.isPreloaded(img2.src), img2.src + base_msg);
    assert_true(internals.isPreloaded(img3.src), img3.src + base_msg);
    assert_true(internals.isPreloaded(img4.src), img4.src + base_msg);
    assert_true(internals.isPreloaded(img5.src), img5.src + base_msg);
  }, 'all images must be fetched by the preload scanner');

  // Setup the tests described by |priority_tests|.
  for (test of priority_tests) {
    promise_test(async () => {
      const priority = await test.promise;
      assert_equals(priority, test.expected_priority);
    }, test.description);
  }
</script>