TestNG is a testing framework developed in the lines of JUnit and NUnit, however it introduces some new functionalities that make it more powerful and easier to use.
TestNG is designed to cover all categories of tests − unit, functional, end-to-end, integration, etc., and it requires JDK 5 or higher.
This tutorial provides a good understanding on TestNG framework needed to test an enterprise level application to deliver it with robustness and reliability