chromium/src/third_party/blink/web_tests/http/tests/priority-hints/image-dynamic-insertion.html

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

<script>
  const tests = [
    {description: 'high importance on <img>s not fetched by the preload scanner must translate to kHigh resource load priority', importance: 'high', expected_priority: kHigh},
    {description: 'low importance on <img>s not fetched by the preload scanner must translate to kLow resource load priority', importance: 'low', expected_priority: kLow},
    {description: 'auto importance on <img>s not fetched by the preload scanner must have no effect on resource load priority', importance: 'auto', expected_priority: kLow},
    {description: 'invalid importance on <img>s not fetched by the preload scanner must have no effect on resource load priority', importance: 'xyz', expected_priority: kLow},
    {description: 'missing importance on <img>s not fetched by the preload scanner must have no effect on resource load priority', expected_priority: kLow}
  ];

  let iteration = 0;
  for (const test of tests) {
    promise_test(async () => {
      const img = document.createElement('img');
      img.alt = 'img';
      if (test.importance) img.importance = test.importance;

      const url = new URL(`../resources/square.png?${iteration++}`, location);
      const priorityPromise = internals.getResourcePriority(url, document);
      img.src = url;
      const priority = await priorityPromise;
      assert_equals(priority, test.expected_priority, test.description);
    });
  }
</script>