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