TestNG is a testing framework for Java mainly used for automation testing. It is similar to Junit but has more features like annotations, parallel execution& grouping tests.

It's used for running tests, generating reports, and organizing test execution. TestNG stands for Test Next Generation, and it’s widely used in unit testing, integration testing, and end-to-end testing.

Key Features of TestNG:

Annotations: Annotations are special markers with ‘@’ used before methods to control test execution. (i.e. Which method runs first and which method run at last etc.) .These annotations are more flexible than JUnit’s.
- @Test: Marks a method as a test method.
- @BeforeSuite, @AfterSuite: Methods that run before and after the entire suite.
- @BeforeTest, @AfterTest: Methods that run before and after each test tag.
- @BeforeMethod, @AfterMethod: Methods that run before and after each test method.
- @DataProvider: Used for providing test data to methods.
Parallel Test Execution: TestNG allows you to run tests in parallel, which helps speed up the testing process, especially when running large test suites.
Group Testing: With TestNG, you can group tests together and execute them as a set, or include/exclude certain groups based on the test case.
Test Configuration: It provides configurations such as retrying failed tests, specifying the order of test execution, and handling test dependencies.
XML Configuration: TestNG uses an XML file (testng.xml) for running tests. This XML configuration provides a lot of flexibility, such as running tests in a specific order, setting up parallel execution, and grouping tests.
Reporting: TestNG generates detailed reports after running tests, which include pass/fail results, test duration, etc. These reports help you analyze test results quickly.
Assertions: TestNG supports assertions that you can use in your test methods to verify the output of your tests. For example:
- assertTrue(), assertFalse(), assertEquals(), etc.
Test Dependencies: TestNG supports specifying dependencies between tests. This is useful when a test depends on another test to pass before it runs.

Benefits of Using TestNG:

Flexibility in test execution (parallel execution, grouping, etc.)
Detailed reports help with better test tracking and debugging.
Powerful annotations make test configuration easier.
Easy integration with build tools like Maven and Gradle.
Can be integrated with Selenium for automating web application tests.

Why Use TestNG?

Simple to Use: TestNG has easy-to-understand annotations and provides a straightforward way to organize tests.
Advanced Features: It supports advanced features such as parallel test execution, test configuration, and dependency management, which is useful for larger projects.
Integration: TestNG integrates well with build tools like Maven and Gradle, as well as continuous integration tools like Jenkins.
Flexible Reporting: The detailed reports help you easily track which tests passed, failed, or were skipped, and provide logs for troubleshooting.

Example of How It Works:

You can write a test in a Java method and annotate it with @Test. This tells TestNG that this method is a test to be run.
TestNG will run your test, check the results, and give you a report showing if your test passed or failed.

Important TestNG Annotations:

@Test: Marks a method as a test method.
@BeforeMethod: Runs before each test method.
@AfterMethod: Runs after each test method.
@BeforeClass: Runs once before the first method in the class.
@AfterClass: Runs once after the last method in the class.
@BeforeSuite: Runs once before all test methods in the suite.
@AfterSuite: Runs once after all test methods in the suite.
@DataProvider: Provides a method with multiple sets of data to test with.

Introduction to TestNG Framework