Practice: Migrate to JUnit 5

Ready to practice migrating from JUnit 4 to JUnit 5? We've prepared a test class with common JUnit 4 patterns that you can improve.

Exercise: OrderValidatorTest

The OrderValidatorTest class in the orders module demonstrates several JUnit 4 patterns that need migration:

What you'll find

• ❌ JUnit 4 annotations: @Before, @Test from org.junit.
• ❌ Try-catch-fail pattern: Awkward exception testing with try-catch blocks.
• ❌ Verbose assertions: Manual loops and checks.
• ❌ Old assertion style: JUnit 4's assertTrue, assertEquals, assertFalse.

Your task

Migrate this test to JUnit 5 and improve the test patterns.

Hints:

• Look at the Migrate to JUnit 5 page for guidance on package and annotation changes.
• JUnit 5 uses different package names (org.junit.jupiter.api.* instead of org.junit.*).
• Lifecycle annotations have new names that better express their purpose.
• Exception testing can be done more elegantly without try-catch blocks.
• JUnit 5 relaxes visibility requirements for test classes and methods.

Running the test

You can run the test in your IDE or use the following commands:

# Run the test
mvn test -pl orders -Dtest=OrderValidatorTest

# Or run all tests in the orders module
mvn test -pl orders

Automated migration

By completing this exercise, you'll gain hands-on experience with:

• Converting JUnit 4 lifecycle annotations to JUnit 5.
• Modernizing exception testing patterns.
• Improving test readability and maintainability.
• Understanding the benefits of JUnit 5 over JUnit 4.

Running the migration recipes

You can also use OpenRewrite to automatically migrate the test:

Moderne CLI

The Moderne CLI allows you to run OpenRewrite recipes on your project without needing to modify your build files, against serialized Lossless Semantic Tree (LST) of your project for a considerable performance boost & across projects.

You will need to have configured the Moderne CLI on your machine before you can run the following command.

1. If project serialized Lossless Semantic Tree is not yet available locally, then build the LST. This is only needed the first time, or after extensive changes:

shell

mod build ~/workspace/

2. If the recipe is not available locally yet, then you can install it once using:

shell

mod config recipes jar install org.openrewrite.recipe:rewrite-testing-frameworks:LATEST

3. Run the recipe.

shell

mod run ~/workspace/ --recipe org.openrewrite.java.testing.junit5.JUnit4to5Migration

Maven Command Line

You will need to have Maven installed on your machine before you can run the following command.

shell

mvn -U org.openrewrite.maven:rewrite-maven-plugin:run -Drewrite.recipeArtifactCoordinates=org.openrewrite.recipe:rewrite-testing-frameworks:RELEASE -Drewrite.activeRecipes=org.openrewrite.java.testing.junit5.JUnit4to5Migration -Drewrite.exportDatatables=true

Maven POM

You may add the plugin to your pom.xml file, so that it is available for all developers and CI/CD pipelines.

1. Add the following to your pom.xml file:

pom.xml

<project>
  <build>
    <plugins>
      <plugin>
        <groupId>org.openrewrite.maven</groupId>
        <artifactId>rewrite-maven-plugin</artifactId>
        <version>LATEST</version>
        <configuration>
          <exportDatatables>true</exportDatatables>
          <activeRecipes>
            <recipe>org.openrewrite.java.testing.junit5.JUnit4to5Migration</recipe>
          </activeRecipes>
        </configuration>
        <dependencies>
          <dependency>
            <groupId>org.openrewrite.recipe</groupId>
            <artifactId>rewrite-testing-frameworks</artifactId>
            <version>LATEST</version>
          </dependency>
        </dependencies>
      </plugin>
    </plugins>
  </build>
</project>

2. Run the recipe.

shell

mvn rewrite:run

Gradle init script

Gradle init scripts are a good way to try out a recipe without modifying your build.gradle file.

1. Create a file named init.gradle in the root of your project.

init.gradle

initscript {
    repositories {
        maven { url "https://plugins.gradle.org/m2" }
    }
    dependencies { classpath("org.openrewrite:plugin:latest.release") }
}
rootProject {
    plugins.apply(org.openrewrite.gradle.RewritePlugin)
    dependencies {
        rewrite("org.openrewrite.recipe:rewrite-testing-frameworks:latest.release")
    }
    rewrite {
        activeRecipe("org.openrewrite.java.testing.junit5.JUnit4to5Migration")
        setExportDatatables(true)
    }
    afterEvaluate {
        if (repositories.isEmpty()) {
            repositories {
                mavenCentral()
            }
        }
    }
}

2. Run the recipe.

shell

gradle --init-script init.gradle rewriteRun

Gradle

You can add the plugin to your build.gradle file, so that it is available for all developers and CI/CD pipelines.

1. Add the following to your build.gradle file:

build.gradle

plugins {
    id("org.openrewrite.rewrite") version("latest.release")
}

rewrite {
    activeRecipe("org.openrewrite.java.testing.junit5.JUnit4to5Migration")
    setExportDatatables(true)
}

repositories {
    mavenCentral()
}

dependencies {
    rewrite("org.openrewrite.recipe:rewrite-testing-frameworks:latest.release")
}

2. Run gradle rewriteRun to run the recipe.

IntelliJ IDEA Ultimate

You can run OpenRewrite recipes directly from IntelliJ IDEA Ultimate, by adding a rewrite.yml file to your project.

rewrite.yml

---
type: specs.openrewrite.org/v1beta/recipe
name: com.github.timtebeek.AdoptJUnitJupiter
displayName: Adopt JUnit Jupiter
description: Adopt JUnit Jupiter and apply best practices to assertions.
recipeList:
  - org.openrewrite.java.testing.junit5.JUnit4to5Migration

After adding the file, you should see a run icon in the left margin offering to run the recipe.

See the Migrate to JUnit 5 page for more migration options.