TestNG

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:

	//This method will provide data to any test method that declares that its Data Provider is named "provider1". 
	@DataProvider(name = "provider1")
	public Object[][] createData1() {
		return new Object[][] { 
			{ "Cedric", new Integer(36) },
			{ "Anne", new Integer(37) }
		};
	}

	// This test method declares that its data should be supplied by the Data Provider named "provider1".
	@Test(dataProvider = "provider1")
	public void verifyData1(String n1, Integer n2) {
		System.out.println(n1 + " " + n2);
	}

	// A data provider which returns an iterator of parameter arrays.
	@DataProvider(name = "provider2")
	public Iterator<Object[]> createData() {
		return new MyIterator(...);
	}	

	// A data provider with an argument of the type java.lang.reflect.Method.
	// It is particularly useful when several test methods use the same 
	// provider and you want it to return different values depending on 
	// which test method it is serving. 
	@DataProvider(name = "provider3")
	public Object[][] createData(Method m) {
		System.out.println(m.getName()); 
		return new Object[][] { new Object[] { "Cedric" } };
	}

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

• An array of array of objects (Object[][]) where the first dimension's size is the number of times the test method will be invoked and the second dimension size contains an array of objects that must be compatible with the parameter types of the test method.
• An Iterator<Object[]>. The only difference with Object[][] is that an Iterator lets you create your test data lazily. TestNG will invoke the iterator and then the test method with the parameters returned by this iterator one by one. This is particularly useful if you have a lot of parameter sets to pass to the method and you don't want to create all of them upfront.

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^[3] to generate reports similar to those obtained when using JUnit. Since version 4.6, TestNG also provides a reporter API^[4] that permits third-party report generators, such as ReportNG,^[5] PDFngreport^[6] and TestNG-XSLT,^[7] to be used.

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.