JUnit 5 in Practice

A test that fails with expected: <true> but was: <false> in a method called testCalcul2 costs you fifteen minutes: you have to open the file, reread the setup, and reconstruct the author's intent. The same test, named un_retrait_superieur_au_solde_est_refuse and ending with an AssertJ assertion that prints the full object, costs you five seconds. The difference is not cosmetic. It determines whether your suite is a diagnostic tool or an alarm with no context.

JUnit 5 is not an incremental version of JUnit 4: it is a rewrite, with a new package (org.junit.jupiter), a new extension model, and an explicit lifecycle. The most common confusion comes from this: org.junit.Test and org.junit.jupiter.api.Test often coexist in the same project, and a class annotated with the old one is simply ignored by the new engine. It doesn't break, it disappears. Always check the number of tests executed after a migration.

Setup

With Maven, a single dependency is enough; recent versions of surefire detect JUnit 5 without any configuration.

<dependencies>
    <dependency>
        <groupId>org.junit.jupiter</groupId>
        <artifactId>junit-jupiter</artifactId>
        <version>5.11.3</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.assertj</groupId>
        <artifactId>assertj-core</artifactId>
        <version>3.26.3</version>
        <scope>test</scope>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-surefire-plugin</artifactId>
            <version>3.5.2</version>
        </plugin>
    </plugins>
</build>