How to test Exceptions using Java JUnit

Let us take a look at how to test exceptions using Junit.

package org.code2care;

public class Calculation {

	public int divide(int no1, int no2) {
		return no1 / no2;
	}

	public void numberToString(int no) {
		System.out.println("The no. entered is: " + Integer.toString(no));

	}
}

package org.code2care;

public class CalculationClient {
	
	public static void main(String[] args) {
		
		Calculation cal = new Calculation();
		
		Integer no1 = 20;
		Integer no2 = 10;
		
		System.out.println(cal.divide(no1, no2));
		cal.numberToString(no2);
		
	}

}

We have two methods division that can throw ArithmeticException and numberToString that can throw a NullPointerException

Let's write test cases in Java JUnit to test these exceptions.

package myprog;

import org.code2care.Calculation;
import org.junit.Test;

/**
 * 
 * JUnit test cases for
 * testing exceptions
 * 
 * @author code2care
 *
 */
public class CalculationTest {

	@Test(expected = ArithmeticException.class)
	public void divideTwoNumbersArithmeticExceptionTest() {
		Calculation calculation = new Calculation();
		int no1 = 20;
		int no2 = 0;
		calculation.divide(no1, no2);
	}

	@Test(expected = NullPointerException.class)
	public void noToStringNullPointerExceptionText() {
		Calculation calculation = new Calculation();
		Integer no1 = null;
		calculation.numberToString(no1);
	}

}