Over a million developers have joined DZone.

Introduction to Unit Testing Using JUnit4 on NetBeans IDE

DZone 's Guide to

Introduction to Unit Testing Using JUnit4 on NetBeans IDE

Learn how to use JUnit for unit testing with the NetBeans IDE to improve code quality.

· Performance Zone ·
Free Resource

JUnit Hello World in NetBeans IDE

This article is intended for Java developers with basic knowledge of core Java and Object Oriented Principles. You need not be familiar with JUnit framework or NetBeans IDE to follow this article.

This article provides an introduction to the test-first, or test-driven, development (TDD) philosophy which recommends that unit testing and coding should go hand-in-hand to ensure the stability of your code.

This is an actionable article which guides a user to write a very simple unit test while developing a simple application. It would hardly take 10 minutes for a beginner level Java developer to try out the code in this article.

Generally, it takes a couple of years for a Java developer working on professional projects to appreciate the benefits of writing unit tests for his/her code. Even the NetBeans documentation on creating Unit test requires familiarity with Java Collections classes. This article demonstrates the benefit of Unit testing with very less effort and would immediately encourage developers in getting in to the habit of writing unit tests simultaneously with production code.

What Is JUnit?

JUnit is a simple, free and open source framework to write repeatable unit tests using Java. Erick Gamma and Kert Beck originally wrote it. It is a regression-testing framework, which allows the developer to write code faster with high quality. JUnit tests increase the stability of the software.

The main philosophy behind this testing framework is to make coding and testing move hand in hand.

NetBeans IDE Overview

In this article, we will apply this philosophy of testing and coding side by side to an object-oriented version of Hello World program by creating a test case for it in NetBeans IDE. NetBeans IDE is the official IDE for Java 8 for development of desktop, mobile, and web applications, as well as HTML5 (including Oracle JET) applications with HTML, JavaScript, and CSS.

Let us apply this philosophy of testing and coding side by side to the object-oriented version of Hello World program by creating a test case for it in NetBeans IDE v8.2. It available for free download from this URL.

Writing Java and Test Classes Using NetBeans IDE

Please follow the steps below:

  1. Launch NetBeans IDE. In Windows 10, it can be started using > NetBeans > NetBeans 8.2 IDE.
  2. In the IDE, choose File > New Project, as shown in the figure below.

Image title

3. In the New Project wizard, expand the Java category and select Java Application as shown in the figure below. Then click Next.

Image title

4. In the Name and Location page of the wizard, do the following (as shown in the figure below):

  • In the Project Name field, type HelloWorld.
  • Check the Use Dedicated Folder for Storing Libraries checkbox.
  • In the Create Main Class field, type com.dzone.example.HelloWorld

Image title

5. Click Finish to create the project.

6. Now go to context menu of the project and Select New > Java Class… to create a new Java class.

Image title

6. Type in the following code for the class.

package com.oracle.hgbu.example;

 * An Object Oriented Hello World Program.  
 * @version 1.0 
public class HelloWorld {  
  private String hello; 
  private String world;         

  * Constructor         
    hello = “Hello”;  
    world = “World”; 

  * forms the Hello World Message.          
  public String formMessage(){ 
 String message;  
    message = hello + ” ” +  world;  
    return message; 

  public static void main(String[] args) {  
    HelloWorld helloWorld = new HelloWorld();  

7. Now select New File... from the context menu of the Project and Choose Test for Existing Class.

Image title

8. Enter the following details and Click Next.

Image title

See below the project structure for your reference.

Image title

9. Now select the HelloWorld.java from Browse… as shown in the figure below and click Finish.

Image title

10. Write the following code for the HelloWorldTest class.

package com.oracle.hgbu.example;

import org.junit.After;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;

 * Test class for HelloWorld 
 * @version 1.0
public class HelloWorldTest {

    HelloWorld helloWorldInstance;

    public void setUp() {
        System.out.println("* HelloWorldTest: Before method setUp()");
        helloWorldInstance = new HelloWorld();        

    public void tearDown() {
        System.out.println("* HelloWorldTest: After method tearDown()");
        helloWorldInstance = null;
    * unit test for formMessage method.         
    public void testFormMessage() {
        //Asserts that two Strings are equal                
        String expResult = "Hello World!";
        String result = helloWorldInstance.formMessage();
        System.out.println("* HelloWorldTest: test method 1 testFormMessage()");
         Assert.assertEquals(expResult, result);

11. Select Test from the context menu of the project or press (Alt + F6).

Image title

Congrats, the green bar indicates that the test is successful. If the test case fails, a red bar and error message are displayed.

12. Now select Run from the context menu of the project to Run the Hello World Program.

Image title

The string “Hello World” is printed to the console. This finishes the Hello World program with Unit Test in NetBeans IDE.

JUnit Best Practices

Below are some of the best practices I would recommend while using JUnit in production:

  • Run all the tests in the system at least once per day (or night).
  • If you find yourself debugging using System.out.println(), better write a test to automatically check the result instead.
  • When a bug is reported, write a test to expose the bug.
  • Write unit tests before writing the code and only write new code when a test is failing.

In the next article, I would be writing about more tips and tricks for improving your code quality.

java ,junit 4 ,netbeans ide ,code quality ,unit testing ,tutorial ,performance

Opinions expressed by DZone contributors are their own.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}