Run a Python web server in the current directory with the following command line and access /framing.html with a web browser.
python -m http.server --cgi
The file framing.html includes an iframe element that points to /cgi-bin/subframe.py. Comment various lines in this script to test the Content-Security-Policy headers in your browsers. Make sure your force a refresh with Ctrl+F5 or Ctrl-R to reload the full page before each test.
The file subframe.html is a static page that can only be used to test the <meta> if there are issues with running the CGI script.