jUnit 6, part 4: automated testing from the command line

When developing a stand-alone Java program all by yourself, it's typically preferable to do so from an IDE. However, a lot of projects rely on automated compiling and testing and this is really best done from the command line. While you may be used to using jUnit from inside an IDE like IntelliJ, it can also be used from the command line using the "Platform Console" application, also known as "Console Launcher".

One use case scenario is this: you're working on a group project and each of you is updating code to a central repository. Each time one of your teammates updates the repository and you synch the repo with your local set of files, you'll want to make sure that the code works as it did before. So once you've downloaded from the repo, you run the jUnit Platform Console, from the command line.

Another use case scenario could go like this: you're working on a live project and you've made an update to the code base and want to make sure that your code works before shipping it to the client. Run jUnit Platform Console.

Both of these use cases are pretty standard and traditional. There's a new one that's become important lately. What if you have an AI agent writing code? Either you or the agent could access jUnit Platform Console to check the agent's work before committing it to the repository. (I'm not advocating for you to do agentic coding, whether in school or at work. AI is hyper-problematic for all kinds of reasons!)

As for me, as a programming instructor, I can see this being really useful in the automation of testing of student assignments and exams, similar to what I used to do with Virtual Programming Lab on YorkU's eClass system.

Regardless of your specific reason, the automation of testing is a really important part of engineering. Moss, on YouTube, has a playlist of Java test automation for jUnit 5. His videos date back a few years, but I'm sure that a lot of it is applicable to jUnit 6. Just in case I'm going to go through the steps of setting up automated testing with the jUnit 6 to make sure to incorporate any relevant changes. I'll start with a basic verification with a simple test class, described below.

Step 1: Download Platform Console JAR

Here I'll be using OpenJDK 27 and jUnit 6. Specifically, I'll be using version 6.1.0 of jUnit's Platform Console, which can be downloaded as a JAR from the Maven Repository:

• Platform Console standalone JAR version 6.1.0 @ Maven Repository.

Once I've downloaded the JAR file, I'll place it into a folder, like simpleTest/ in my Downloads folder. In my case the file is called junit-platform-console-standalone-6.1.0.jar.

My example is tested on a macOS machine (m3 Pro) but it should also work on Linux and in Windows PowerShell.

Step 2: Write a simple jUnit test class

Then, using a text editor, in that same simpleTest/ folder, write and save a trivial jUnit testing file, TestSimpleClass.java:

// TestSimpleClass.java
import static org.junit.jupiter.api.Assertions.assertTrue;
import org.junit.jupiter.api.Test;

class TestSimpleClass {
    
    @Test
    void testMethod() {  
        assertTrue(true);
    }
}

Inside this class is a single test that contains a single method that calls the assertTrue(). It should always result in a true test evaluation.

(Note: you don't have to write this file within the terminal. You can write it in your favourite GUI text editor, instead)

Step 3: Compile the jUnit test class

Now, this part needs to be done from within the terminal. Put yourself in the correct directory (like simpleTest/) and type the following:

javac -cp junit-platform-console-standalone-6.1.0.jar TestSimpleClass.java

This has the effect of explicitly including the Platform Console JAR file in the class path during the compilation of TestSimpleClass.java. This will create the compiled TestSimpleClass.class file.

Why is the platform console JAR file included? Because regular Java doesn't have jUnit built in. Instead, we need to import the jUnit tools, as shown by the two import lines in the source file. It turns out that the Platform Console JAR file is capable of supplying those dependencies, so we use it to do so.

Step 4: Discover Containers and Test(s)

Next, we want to see if Platform Console can identify all the important parts needed to run the unit test(s). We will need to see at least four "containers" and one "test". To do this we run the "discover" option on the Platform Console JAR file and apply within the current folder (class path is "dot") and to the class file found within this folder:

java -jar junit-platform-console-standalone-6.1.0.jar discover --class-path "." --select-class TestSimpleClass 

This should output something like this:

What this shows us is that four containers have been found: Platform Suite, Jupiter, Vintage and TestSimpleClass. The first three are standard are included in the Platform Console JAR file. It's the fourth one, TestSimpleClass, that's critical. It's the fourth container. Just as important, we see that the testMethod within the class, has been identified. This is the test. We're now ready to execute.

Step 5: Execute the Unit Test(s)

Now that you're confident that the unit test is discoverable by jUnit, it's time to execute the single test in my Java class file works as designed. To do that I replaced the word "discover" with "execute" in the command I used previously.

java -jar junit-platform-console-standalone-6.1.0.jar execute --class-path "." --select-class TestSimpleClass

As we can see above, the Execute output is similar to the Discover output. The difference is that it ran the test and the test return a positive (successful) result. On non-trivial unit tests it won't always be successful. But that's not what's important. What's important is that the test ran.

Further Reading

As people predict the demise of programming due to AI, there are many in the engineering and computer science fields who are seeing, instead a shift of priorities. For example, as Patricia Aas puts it, "I think that QAs [Quality Assurance engineers and technicians] have a bright future". (more and QA and testing here) More generally, as Dave Farley of the Modern Software Engineering channel says, it's that software engineering is really about "understanding, designing, testing, and integrating solutions to real-world problems".

Really, this isn't new. These priorities have always been around, but they just weren't as exciting to a lot of people as writing actual code. So, for some it's a shift in priorities. For others, it's a confirmation that the "real work" was never the coding. Instead it was about processes that help ensure success of a project or product. And that doesn't change with AI.

Conclusion

The Platform Console for jUnit 6 works, both at the discovery stage and the execution stage. This opens up all kinds of possibilities.

Edits

June 16, 2026: added the Further Reading section to add some context for deeper diving.

June 16, 2026: added a new comment.

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James Andrew Smith is a Professional Engineer and Associate Professor in the Electrical Engineering and Computer Science Department of York University’s Lassonde School, with degrees in Electrical and Mechanical Engineering from the University of Alberta and McGill University.  Previously a program director in biomedical engineering, his research background spans robotics, locomotion, human birth, music and engineering education. While on sabbatical in 2018-19 with his wife and kids he lived in Strasbourg, France and he taught at the INSA Strasbourg and Hochschule Karlsruhe and wrote about his personal and professional perspectives.  James is a proponent of using social media to advocate for justice, equity, diversity and inclusion as well as evidence-based applications of research in the public sphere. You can find him on Twitter.  You can find him on BlueSky. Originally from Québec City, he now lives in Toronto, Canada. 

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