HTTP/2 is becoming more and more popular… below are a few collected links, for future reference.
Tools for testing a server / website:
https://tools.keycdn.com/http2-test
https://gtmetrix.com/
Testing a client / browsers:
https://http2.akamai.com/demo
https://www.httpvshttps.com/
Firefox plug-in showing SPDY and HTTP/2 status:
https://addons.mozilla.org/en-US/firefox/addon/spdy-indicator/
By the way, a few tools for general website analysis:
https://gtmetrix.com/
http://www.webpagetest.org/
https://developers.google.com/speed/pagespeed/insights/
http://tools.pingdom.com/fpt/
Does it use GZIP compression: