It’s used to test the exception throw by the method.

import org.testng.annotations.*;
 
/**
 * TestNG Expected Exception Test
 * @author mkyong
 *
 */
public class TestNGTest2 {
 
	@Test(expectedExceptions = ArithmeticException.class)  
	public void divisionWithException() {  
	  int i = 1/0;
	}  
 
}

In above example, the divisionWithException() method will throw an ArithmeticException Exception, since this is an expected exception, so the unit test will pass.