In this post we will learn how to use TestNG expectedExceptions feature to test the expected exception your code might throw in certain situations. We can annotate a test method with particular exception information using @Test(expectedExceptions = Exception.class) if we know that the method will throw this kind of exception during execution. Let’s get going.

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Let’s take a simple Calculator class to demonstrate this feature.

package com.websystique.testng;

public class Calculator {

 public int add(int  a, int b){
  return a+b;
 }
 
 public int divide(int a, int b){
  return a/b;
 }

}

We know that divide method will throw an ArithmaticException if second argument is 0.

Let’s write a sample test class to test calculator class.

package com.websystique.testng;

import org.testng.Assert;
import org.testng.annotations.AfterClass;
import org.testng.annotations.BeforeClass;
import org.testng.annotations.Test;

public class TestNgExpectedExceptionsExample {

 Calculator calculator;

 @BeforeClass
 public void setup() {
  System.out.println("setup()");
  calculator = new Calculator();
 }

 @AfterClass
 public void tearDown() {
  System.out.println("tearDown()");
  calculator = null;
 }


 @Test
 public void testAdd() {
  System.out.println("testAdd()");
  Assert.assertEquals(calculator.add(3, 4), 7);
 }

 @Test
 public void testDivide() {
  System.out.println("testDivide()");
  Assert.assertEquals(calculator.divide(16, 4), 4);
 }
 
 @Test(expectedExceptions = ArithmeticException.class)
 public void testDivideByZero() {
  System.out.println("testDivideByZero()");
  Assert.assertEquals(calculator.divide(16, 0), 12345);
 }
 

}

testAdd and TestDevide are basic tests. testDevideByZero is special in that it is passing 0 as second argument in calculator.divide() method, which will certainly throw an ArithmeticException. We can specify the particular exception we expect this method to throw using expectedExceptions attribute in @Test annotation like we did @Test(expectedExceptions = ArithmeticException.class).

Run above test class using TestNG Eclipse plugin or maven (mvn clean test). Following is the outcome:

setup()
testAdd()
testDivide()
testDivideByZero()
tearDown()
PASSED: testAdd
PASSED: testDivide
PASSED: testDivideByZero

===============================================
    Default test
    Tests run: 3, Failures: 0, Skips: 0
===============================================

Test testDivideByZero passed successfully despite throwing exception because we informed TestNG that this particular exception is expected behavior.

That’s it.

References

• TestNG Official Reference
• TestNG Javadocs
• TestNG Eclipse Plugin
• Maven surefire plugin