Executing JUnit 4 and JUnit 5 tests in a same build

Question

In Maven projects, I have some existing tests relying on JUnit 4. I cannot migrate these tests in JUnit 5 for multiple reasons.
Essentially, some tests depend on a library which uses JUnit 4 runner and code migration may take time.

I would like all the same create new test classes with JUnit 5 that is now released and provides new interesting features.
How to do that ?

Answer 1

JUnit 5 provides a way out of the box.

JUnit 5 = JUnit Platform + JUnit Jupiter + JUnit Vintage

Each one is a distinct project and using all of them allows to compile and execute JUnit 4 and JUnit 5 tests in a same project.

JUnit Jupiter is the combination of the new programming model and extension model for writing tests and extensions in JUnit 5.

JUnit Vintage provides a TestEngine for running JUnit 3 and JUnit 4 based tests on the platform.

The JUnit Platform serves as a foundation for launching testing frameworks on the JVM

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Update : from Maven Surefire 2.22.0

From the JUnit 5 documentation :

Starting with version 2.22.0, Maven Surefire provides native support for executing tests on the JUnit Platform.

So the configuration is much simpler.
Note that the junit-4 api dependency is optional as the engine dependencies that are now required already pull a default api version (it is the case for both junit 4 and 5).

Here is a sample pom.xml.

<project xmlns="http://maven.apache.org/POM/4.0.0"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">     <modelVersion>4.0.0</modelVersion>     <groupId>david</groupId>     <artifactId>jupiter-4-and-5-same-build</artifactId>     <version>0.0.1-SNAPSHOT</version>      <properties>         <maven.compiler.source>1.8</maven.compiler.source>         <maven.compiler.target>1.8</maven.compiler.target>         <junit-jupiter.version>5.1.0</junit-jupiter.version>         <!-- optional : if we want to use a junit4 specific version -->         <junit.version>4.12</junit.version>     </properties>     <dependencies>         <!--JUnit Jupiter Engine to depend on the JUnit5 engine and JUnit 5 API -->         <dependency>             <groupId>org.junit.jupiter</groupId>             <artifactId>junit-jupiter-engine</artifactId>             <version>${junit-jupiter.version}</version>             <scope>test</scope>         </dependency>         <!--JUnit Jupiter Engine to depend on the JUnit4 engine and JUnit 4 API  -->         <dependency>             <groupId>org.junit.vintage</groupId>             <artifactId>junit-vintage-engine</artifactId>             <version>${junit-jupiter.version}</version>         </dependency>         <!-- Optional : override the JUnit 4 API version provided by junit-vintage-engine -->         <dependency>             <groupId>junit</groupId>             <artifactId>junit</artifactId>             <version>${junit.version}</version>             <scope>test</scope>         </dependency>     </dependencies>      <build>         <plugins>             <plugin>                 <artifactId>maven-surefire-plugin</artifactId>                 <version>2.22.0</version>             </plugin>         </plugins>     </build>  </project> 

On my GitHub space I added a working sample maven project that you can browse/clone. URL: https://github.com/ebundy/junit4-and-5-minimal-maven-project

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Old way : for Maven Surefire below 2.22.0

Here is the minimal configuration to use with Maven to configure the project to compile and run both JUnit4 and JUnit5 tests :

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">     <modelVersion>4.0.0</modelVersion>     <groupId>mygroup</groupId>     <artifactId>minimal-conf-junit4-5</artifactId>     <version>0.0.1-SNAPSHOT</version>      <properties>         <!-- JUnit 5 depends on JDK 1.8 -->         <maven.compiler.source>1.8</maven.compiler.source>         <maven.compiler.target>1.8</maven.compiler.target>         <!--  JUnit dependency versions -->         <junit.version>4.12</junit.version>         <junit-vintage-engine>4.12.1</junit-vintage-engine>         <junit-jupiter.version>5.0.1</junit-jupiter.version>         <junit-platform.version>1.0.1</junit-platform.version>     </properties>      <dependencies>         <!--JUnit Jupiter API to write and compile tests with JUnit5 -->         <dependency>             <groupId>org.junit.jupiter</groupId>             <artifactId>junit-jupiter-api</artifactId>             <version>${junit-jupiter.version}</version>             <scope>test</scope>         </dependency>         <!-- JUnit 4 to make legacy JUnit 4 tests compile -->         <dependency>             <groupId>junit</groupId>             <artifactId>junit</artifactId>             <version>${junit.version}</version>             <scope>test</scope>         </dependency>     </dependencies>      <build>         <plugins>             <plugin>                 <artifactId>maven-surefire-plugin</artifactId>                 <version>2.19.1</version> <!-- matters until now-->                 <dependencies>                     <!-- to let surefire to run JUnit 4 but also JUnit 5 tests -->                     <dependency>                         <groupId>org.junit.platform</groupId>                         <artifactId>junit-platform-surefire-provider</artifactId>                         <version>${junit-platform.version}</version>                     </dependency>                     <!-- JUnit vintage engine to run JUnit 3 or JUnit 4 tests -->                     <dependency>                         <groupId>org.junit.vintage</groupId>                         <artifactId>junit-vintage-engine</artifactId>                         <version>${junit-vintage-engine}</version>                     </dependency>                     <!-- JUnit 5 engine to run JUnit 5 tests -->                     <dependency>                         <groupId>org.junit.jupiter</groupId>                         <artifactId>junit-jupiter-engine</artifactId>                         <version>${junit-jupiter.version}</version>                     </dependency>                 </dependencies>             </plugin>         </plugins>     </build> </project> 

Now mvn test compiles and runs both JUnit 4 and JUnit 5 tests.

Note 1 : the junit-vintage-engine (4.12.1) and the junit (4.12) dependencies don't specify the same exact version.
This is not an issue at all as :

• their release are not related between them

• junit-vintage-engine is designed to run any JUnit 3 or 4 tests.
  

Note 2 : maven-surefire-plugin with the 2.19.1 version matters whatever you want to compile JUnit 5 test classes or both JUnit 4 and JUnit 5 test classes.
Next version of the plugin causes indeed some exceptions during JUnit 5 tests execution but the 2.22.0 that at last solves the issue (see the first part of the answer : "Update : from Maven Surefire 2.22.0").

Answer 2

JUnit have a number of example projects at https://github.com/junit-team/junit5-samples

I had a Gradle project and following https://github.com/junit-team/junit5-samples/tree/main/junit5-migration-gradle worked for me.

https://github.com/junit-team/junit5-samples/tree/main/junit5-migration-maven is the Maven equivalent - I have not tried it but I imagine that it works too.