mozilla-release/testing/web-platform/tests/page-visibility/test_attributes_exist.html

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <title>Page Visibility API Definition</title>

        <script type="text/javascript" src="/resources/testharness.js"></script>
        <script src="/resources/testharnessreport.js"></script>
        <script type="text/javascript" src="resources/pagevistestharness.js"></script>
    </head>
    <body>
        <h1>Description</h1>
        <p>This test validates that all of the attributes associated with the Page Visibility feature exist
           (but does not validate that their values are correct).</p>

        <div id="log"></div>

        <script type="text/javascript" >
            test_feature_exists();
        </script>
    </body>
</html>