All You Need to Know to Implement JUnit Testing in Java

JUnit makes it possible for Java Developers to handle all levels of Java project development. The framework is one of the most popular frameworks used for both unit testing and UI testing. They focus the entire concept of JUnit on testing first and then coding further, making the approach productive and stable. Here, in the article, we will learn how to perform JUnit Testing in Java.

What Is JUnit?

JUnit is an open-source Unit Testing framework for the Java programming language. The term "Unit Testing" refers to the way of testing a unit. 

A unit may be the smallest piece of code that may be fetched from the system. This unit may be a line of the code, a class, or a method. It is better to have as small a code chunk as possible as the tests tend to run faster and provide better insights for small test units.

The JUnit testing framework is widely used by Java developers to write and execute tests. All the test cases have to be re-executed every time a new code is added in order to ensure that nothing is broken. There are graphs in JUnit that represent the progress of the test. When the test runs smoothly, the graph shows green, and when the test fails, it turns red. JUnit Testing makes it possible for developers to develop more reliable and bug-free code.

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Now that the basics of JUnit are clear, let's see how to perform JUnit testing in Java.

JUnit Testing in Java

First, make sure that JUnit is downloaded into your system. Then we will begin with downloading the two Jar files. 

  • Open your browser:
  • In the browser window type “Download JUnit”

  • You will find “About JUnit” as the first option.
  • Go click on that link.
  • There you will find the “Download and Install” option.
  • In that link you will find two jar files:
    • junit.jar
    • Hamcrest.jar
  • Download the two jar files one after the other.


  • Now open the location where those two jar files are downloaded.
  • Copy the two files.
  • Go to your “Documents”.
  • Then open the “Java Library” folder. 
  • Paste the jar files here.

Then in the same folder make a Java file that contains the code that you wish to execute. 

import org.junit.Test;

import org.junit.Ignore

import org.junit.Assert.assertEquals

public class TestJunit {

   String message = “Simplilearn”;


   Public void testPrintMessage() {

      System.out.println(“Inside testPrintMessage()”);

      assertEquals(message, “Simplilearn”);


   Public static void main(String[] argos) {

       TestJunit result = new TestJunit();





The next step is to compile this test file. We will be running the Java program in the command prompt.

  • Open the command prompt 

javac -cp junit-4.13.1.jar;.

java -cp junit-4.13.1.jar;. TestJunit

The javac command is used to convert the .java file to .class file.


The message "Inside testPrintMessage()" on the screen shows that there are no issues with the test case.

Now, to check further, we will make some code changes. We would make the "Simplilearn" in the assertEquals command to be "Simplilearn12".

The new command would be: assertEquals (message, "simplilearn12");

Now, when the commands are again run in the command prompt. We get the output that shows the comparison, which says a "ComparisonFailure".


This is how the JUnit testing works, and a comparison shows what should be put in the application to make the test successful.


By now, you would have gained the knowledge of JUnit Testing and understood what is meant by Unit Testing. Moving forth, you saw how JUnit Testing could be done in Java. In that testing, we used the Command Prompt to compare to show what we could do to correct the code. 

To learn more about this topic, you can begin from the basics with our free Java Training. To become a certified Java developer, you can enroll in our Full Stack Java Developer Master's Program or the Java Certification Training Course.  

About the Author

Ishan GabaIshan Gaba

Ishan Gaba is a Research Analyst at Simplilearn. He is proficient in Java Programming, Data Structures, and Project Management. Graduated in Information Technology, Ishan is also passionate about writing and traveling.

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