https://www.gcreddy.com/2021/02/selenium-online-training.html
TestNG Testing Framework for Selenium, Introduction to TestNG Testing Framework, Install TestNG and write first TestNG Program, Create multiple Test cases & Run, Execute/Run multiple programs using XML, and Data-Driven Testing using @DataProvider annotation.
In Selenium using Java, there two testing frameworks available i. JUnit
ii. TestNG

Note:
Java - JUnit, TestNG
C# - NUnit
Ruby - Repect, Test::Unit
Python - PyUnit, Py:Test

TestNG Testing Framework was designed to simplify a broad range of testing needs from Unit testing to System Testing

Initially, it was developed for Unit Testing, now it is used for all levels of Testing

TestNG is open source software where NG stands for next generation

TestNG inspired by JUnit and NUnit, and introduced some new functionalities

Advantages of TestNG

TestNG annotations are easy to create test cases

Test cases are prioritized more easily

Executes multiple programs using XML

Generates Test Reports