JUnit in BlueJ

Monday, 04.December 2023

JUnit is not part of the Java API, it is a third-party software. You find all information about JUnit, including a user guide and information about and download of the latest version on https://junit.org.

As of this writing, the current version is 5.10.1, but the version included in BlueJ 5.2.1 is JUnit 5.5.2, as you can check within the installation of BlueJ:

BlueJ.app/Contents/Java>ls junit*
junit-4.12.jar				junit-jupiter-params-5.5.2.jar		junit-platform-suite-api-1.5.2.jar
junit-jupiter-5.5.2.jar			junit-platform-commons-1.5.2.jar	junit-vintage-engine-5.5.2.jar
junit-jupiter-api-5.5.2.jar		junit-platform-engine-1.5.2.jar
junit-jupiter-engine-5.5.2.jar		junit-platform-launcher-1.5.2.jar

As we only use a very small portion of JUnit this should not matter - but if you look something up in the BlueJ documentation, keep this in mind. (you could also try updating JUnit in the above directory, of course. I haven’t tried it.)

Also, there have been major changes for writing test cases between JUnit 4 and JUnit 5. You may find old BlueJ-Example projects which still use JUnit 4. As you can see above, both junit-4.12.jar and the vintage engine are included in BlueJ, so they will work. While mixing JUnit 4 and 5 in your source code will work, I recommend migrating old examples to JUnit 5 if you want use them, as anything else will turn out to be confusing. You can tell by the imports which version is used in the examples:

Minimal JUnit imports

JUnit 5 imports

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

Old JUnit 4 imports

import org.junit.Before;
import org.junit.Test;
import static org.junit.Assert.*;

Note that the annotation of the setup method has also changed from @Before to @BeforeEach.