Not able to Install TestNG in Eclipse-Kepler

Go to https://dl.bintray.com/testng-team/testng-eclipse-release/

Click updatesites/

Click any version.

copy resulting URL and use that to install testNG

Example: Use following in eclipse install software. https://dl.bintray.com/testng-team/testng-eclipse-release/updatesites/6.11.0.201703011520/

URL http://beust.com/eclipse/content.xml will forward you to some other location (probably based on your geo location) to site with HTTPS enabled.

This site presented SSL certificate, which is not trusted by your JVM's keystore.

try it!

curl -Lv http://beust.com/eclipse/content.xml

Location: https://dl.bintray.com/testng-team/testng-eclipse-release//content.xml

In your screenshot it is notable by other error:

sun.security.validatorValidatorException : PKIX path building failed

You can try to use this guide to obtain and import site's CA certificate into your JVM's keystore.

But first I would examine this certificate if it's fake or even why JVM didn't recognize it (you are running up-to-date java installation, or not ?)