I am new to learning TestNG. I followed these steps:
The issue is known and already fixed (the fix will be available in the next version): https://github.com/cbeust/testng/pull/1086
As workarround, you can downgrade your testng version or add Guava in your classpath.
It seems below jar is not available in your classpath. com.google.guava_1.6.0.jar
Download from the link below and add it to your classpath.
com.google.guava_1.6.0.jar