mozilla-release/testing/web-platform/tests/content-security-policy/inheritance/iframe-srcdoc-inheritance.html

<!DOCTYPE html>
<head>
  <meta http-equiv="Content-Security-Policy" content="img-src 'self'">
  <script src="/resources/testharness.js"></script>
  <script src="/resources/testharnessreport.js"></script>
</head>
<body>
  <script>
    var t1 = async_test("First image should be blocked");
    var t2 = async_test("Second image should be blocked");
    window.onmessage = t1.step_func_done(function(e) {
      if (e.data == "img blocked") {
        frames[0].frames[0].frameElement.srcdoc =
        `<script>
           window.addEventListener('securitypolicyviolation', function(e) {
             if (e.violatedDirective == 'img-src') {
               top.postMessage('img blocked', '*');
             }
           })
         </scr` + `ipt>
         <img src='/content-security-policy/support/fail.png'
              onload='top.postMessage("img loaded", "*")'/>`;
        window.onmessage = t2.step_func_done(function(e) {
          if (e.data != "img blocked")
            assert_true(false, "The second image should have been blocked");
        });
      } else {
        assert_true(false, "The first image should have been blocked");
      }
    });
  </script>
  <iframe src="support/srcdoc-child-frame.html"></iframe>
</body>
</html>