I didn't understand where we can take a 15 min test and earn a certificate. Can anyone help me?
Okay, so I just took the test, and I can tell that it's not just a shortcut to get a certificate. After you have taken the test, you'll be able to see your certificates in the right part of your homepage. It says the following:
Your certificates Spanish: 3.22/5.0 27 minutes ago
Then you can go to a link(http://www.duolingo.com/certs/793zJj), where you can see the full certificate.