Perform a cross-site request back to
samesitetest.com to test the SameSite cookie attribute:
Cross-site GET request
These links/button initiate a cross-site request back to
which will allow you to see which cookies the browser adds to the request.
Your Browser Developer Tools will allow you to monitor the cookies being sent.
An experiment by Stephen Rees-Carter for "CSRF is dead (or is it?)" and "SameSite Cookies Deep Dive".
Source Code on GitHub, PRs welcome.