chromium/third_party/blink/web_tests/http/tests/eventsource/resources/request-existent-eventsource-error.html

<html>
  <body>
    <script>
      function statusTest(status) {
        var source = new EventSource("status-codes.php?status=" + status);
        source.onerror = function() {
          top.finish();
        }
      }
      statusTest("404");
      statusTest("410");
      statusTest("503");
    </script>
  </body>
</html>