TestNG

Features

TestNG's main features include:

1. Annotation support.
2. Support for parameterized and data-driven testing (with @DataProvider and/or XML configuration).
3. Support for multiple instances of the same test class (with @Factory)
4. Flexible execution model. TestNG can be run either by Ant via build.xml (with or without a test suite defined), or by an IDE plugin with visual results. There isn't a TestSuite class, while test suites, groups and tests selected to run are defined and configured by XML files.
5. Concurrent testing: run tests in arbitrarily big thread pools with various policies available (all methods in their own thread, one thread per test class, etc.), and test whether the code is multithread safe.
6. Embeds BeanShell for further flexibility.
7. Default JDK functions for runtime and logging (no dependencies).
8. Dependent methods for application server testing.
9. Distributed testing: allows distribution of tests on slave machines.

Data Provider

A data provider in TestNG is a method in a test class, which provides an array of varied actual values to dependent test methods.

Example:

The returned type of a data provider can be one of the following two types:

Tool Support

TestNG is supported, out-of-the-box or via plug-ins, by each of the three major Java IDEs - Eclipse, IntelliJ IDEA, and NetBeans. It also comes with a custom task for Apache Ant and is supported by the Maven build system. The Hudson continuous integration server has built-in support for TestNG and is able to track and chart test results over time. Most Java code coverage tools, such as Cobertura, work seamlessly with TestNG.

Reporting

TestNG generates test reports in HTML and XML formats. The XML output can be transformed by the Ant JUnitReport task to generate reports similar to those obtained when using JUnit. Since version 4.6, TestNG also provides a reporter API that permits third-party report generators, such as ReportNG, PDFngreport and TestNG-XSLT, to be used.

Comparison with JUnit

The differences between and respective advantages of the two seemingly competing Java tools, TestNG and JUnit, have been debated throughout the decade. Both camps have strong grounds and supporters. Stackoverflow discussions reflect this controversy.

Annotations

In JUnit 4, the @BeforeClass and @AfterClass methods have to be declared as static. TestNG does not have this constraint.

TestNG has provided four additional setup/teardown pairs for the suite, test and groups, i.e. @BeforeSuite, @AfterSuite, @BeforeTest, @AfterTest, @BeforeGroup and @AfterGroup, @BeforeMethod and @AfterMethod.

Parameterized test

This feature is implemented in both tools, however in quite different ways.

TestNG has two ways for providing varying parameter values to a test method: by setting the testng.xml, and by defining a @DataProvider method.

In JUnit 4, @RunWith and @Parameters are used together to facilitate parameterized tests, while the @Parameters method has to return List[] with all the actual values, which will be fed into a dedicated class constructor as an argument.

Conclusion

JUnit is often shipped with mainstream IDEs by default, which contributes to its wider popularity. However, TestNG's goal is much wider, which includes not only unit testing, but also support of integration and acceptance testing, etc. Which one is better or more suitable depends on use contexts and requirements.