TestNG offers many great features and is definitely more capable as JUnit to build a strong automated Test-Suite. When writing test-cases one important factor is the handling of test-data. With JUnit it is cumbersome to feed different test-data to the same test-code. TestNG solves this much better.

Let’s look at a very simple example. When trying to test an exception with JUnit 4 with different test-data I would need to write something like:

This code has essential problems:

1. Because I want to avoid to write two more test-methods (essentialy the same production code is triggered), I am putting three test-cases into one test-method, which is bad practice. This is because test cases aren’t using the tearDown and setUp facilities and cannot guarantee isolation. That is also the reason that I could not use the excpectedException parameter inside the JUnit 4 @Test annotation. Alternative is to really use three test-methods, but code readability then suffers.
2. Even though above example is very simplified (only new Foo() is called) the test-code is not expressive. Surely you could improve this by extracting method and giving a good name. But still it is a bit blurry, why we do so and that it is just for using different test-data.

TestNG parameterized test-methods

TestNG does it better and builds the “test-case differs only in test-data” situation into its framework. This is done by building a DataProvider and passing parameters to the test-method. This way code gets more expressive and each different test-data set is executed as an isolated test-case also. Here an example of the TestNG version of above test-cases (I followed the code centric way, you can also configure your DataProvider through an XML file):