shadowrootadoptedstylesheets-async-fetch-duplicate.html

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This test has a WPT meta file that expects 1 subtest issues.
This WPT test may be referenced by the following Test IDs:
- /shadow-dom/declarative/tentative/shadowrootadoptedstylesheets/shadowrootadoptedstylesheets-async-fetch-duplicate.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<title>shadowrootadoptedstylesheets: duplicate specifiers are deduplicated</title>

<meta name="author" title="Kurt Catti-Schmidt" href="mailto:kschmi@microsoft.com" />

<link rel='help' href='https://github.com/whatwg/html/pull/11687'>

<script src='/resources/testharness.js'></script>

<script src='/resources/testharnessreport.js'></script>

<script src='./support/helpers.js'></script>

<body>

<script type="module">

  promise_test(async (t) => {

    // The attribute value is parsed as an ordered set of unique space-separated

    // tokens, so duplicate specifiers should result in only one entry.

    const cssUrl = "./support/styles.css?dup";

    const { shadowRoot, testElement } = createStylesheetHost(`${cssUrl} ${cssUrl}`);

    assert_equals(shadowRoot.adoptedStyleSheets.length, 1,

      "Duplicate specifiers should be deduplicated by ordered set parsing.");

    await fetchAndWait(cssUrl);

    assertSheetRule(shadowRoot, 0, "span { color: blue; }", "After fetch");

    assert_equals(getComputedStyle(testElement).color, "rgb(0, 0, 255)",

      "Styles should be applied from the deduplicated specifier.");

  }, "Duplicate specifiers in the attribute are deduplicated.");

</script>

</body>