shadowrootadoptedstylesheets-async-fetch-mutation-clear.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-mutation-clear.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<title>shadowrootadoptedstylesheets mutation: clear all placeholders before fetch</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) => {

    // Clear adoptedStyleSheets entirely before fetch completes.

    const url = "./support/styles-yellow.css";

    const { shadowRoot, testElement } = createStylesheetHost(url);

    assert_equals(shadowRoot.adoptedStyleSheets.length, 1,

      "Before clearing: expected 1 placeholder(s).");

    assert_equals(shadowRoot.adoptedStyleSheets[0].cssRules.length, 0,

      "Before clearing: placeholder at index 0 should be empty.");

    shadowRoot.adoptedStyleSheets = [];

    assert_equals(shadowRoot.adoptedStyleSheets.length, 0,

      "adoptedStyleSheets should be empty after clearing.");

    await fetchAndWait(url);

    assert_equals(shadowRoot.adoptedStyleSheets.length, 0,

      "Cleared placeholder's fetch should not re-insert the sheet.");

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

      "Yellow styles should not be applied after clearing.");

  }, "Clearing adoptedStyleSheets before fetch prevents styles from being applied.");

</script>

</body>