access-control-preflight-headers-sync.htm

<!DOCTYPE html>
<html>
  <head>
    <title>Test that sync CORS requests with custom headers are not sent with OPTIONS preflight</title>
    <script src="/resources/testharness.js"></script>
    <script src="/resources/testharnessreport.js"></script>
    <script src="/common/get-host-info.sub.js"></script>
    <script src="/common/utils.js"></script>
  </head>
  <body>
    <script type="text/javascript">
    test(function() {
      let xhr = new XMLHttpRequest;
      const uuid = token();

      xhr.open("GET", get_host_info().HTTP_REMOTE_ORIGIN +
          "/xhr/resources/reset-token.py?token=" + uuid, false);
      xhr.send();

      xhr = new XMLHttpRequest;
      xhr.open("GET", get_host_info().HTTP_REMOTE_ORIGIN +
          "/xhr/resources/no-custom-header-on-preflight.py?token=" + uuid, false);
      xhr.setRequestHeader("x-test", "foobar");
      xhr.send();
      assert_equals(xhr.responseText, "PASS");
    }, "Preflighted sync request with custom header");
    </script>
  </body>
</html>

chromium/third_party/blink/web_tests/external/wpt/xhr/access-control-preflight-headers-sync.htm