LayoutTests/http/tests/priority-hints/link-dynamic-insertion.html

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="http://127.0.0.1:8000/resources/checkResourcePriority.js"></script>

<script>
  const tests = [
    {description: 'high fetchpriority on <link rel=stylesheet>s not fetched by the preload scanner must load with very high priority', fetchPriority: 'high', expected_priority: "ResourceLoadPriorityVeryHigh"},
    {description: 'low fetchpriority on <link rel=stylesheet>s not fetched by the preload scanner must load with medium priority', fetchPriority: 'low', expected_priority: "ResourceLoadPriorityMedium"},
    {description: 'auto fetchpriority on <link rel=stylesheet>s not fetched by the preload scanner must have no effect on resource load priority', fetchPriority: 'auto', expected_priority: "ResourceLoadPriorityHigh"},
    {description: 'invalid fetchpriority on <link rel=stylesheet>s not fetched by the preload scanner must have no effect on resource load priority', fetchPriority: 'xyz', expected_priority: "ResourceLoadPriorityHigh"},
    {description: 'missing fetchpriority on <link rel=stylesheet>s not fetched by the preload scanner must have no effect on resource load priority', expected_priority: "ResourceLoadPriorityHigh"}
  ];

  let iteration = 0;
  for (const test of tests) {
    async_test(t => {
      const link = document.createElement('link');
      link.rel = 'stylesheet';
      if (test.fetchPriority) link.fetchPriority = test.fetchPriority;
      const url = new URL(`/resources/square100.png?${iteration++}`, location);
      link.href = url;
      link.onload = t.step_func(() => { checkResourcePriority(url, test.expected_priority, test.description); t.done(); });
      document.head.appendChild(link);
    });
  }
</script>