LayoutTests/http/tests/security/sandboxed-iframe-ALLOWED-modals.html

<script>
if (window.testRunner)
    testRunner.dumpAsText();
</script>
<p>This test passes if opening modal dialogs is allowed and no error message is logged in the console.</p>
<iframe sandbox="allow-scripts allow-modals"
        src="data:text/html,<script>
            alert('MESSAGE');
            </script>"></iframe>
<iframe sandbox="allow-scripts allow-modals"
        src="data:text/html,<script>
            confirm('MESSAGE?');
            </script>"></iframe>
<iframe sandbox="allow-scripts allow-modals"
        src="data:text/html,<script>
            prompt('MESSAGE:', 'DEFAULT');
            </script>"></iframe>
<iframe sandbox="allow-scripts allow-modals"
        src="data:text/html,<script>
            print();
            </script>"></iframe>
<iframe sandbox="allow-scripts allow-modals"
        src="data:text/html,<script>
            document.execCommand('print', true, null);
            </script>"></iframe>