Unwanted JUnit 4 Dependency with Kotlin and JUnit 5

I ran across this issue only by accident because I was investigating a completely different problem. I wrote a quick test to debug my issue and was wondering why custom serializers and deserializers are not registered with the Jackson ObjectMapper. I had a nice init() function that was annotated with @Before. So, what the hell?

Let’s back up a bit for some context.

  • Kotlin Project
  • Runs on Java 12
  • JUnit 5 as test engine
  • AssertK for assertions (just for the sake of completeness)

I’m used to JUnit 4, so in my test I used @Before to annotate a setup method. It was one of the many options IntelliJ presented to me.

@Before
fun init() {
    val module = SimpleModule()
    module.addDeserializer(Instant::class.java, InstantDeserializer())
    module.addSerializer(Instant::class.java, InstantSerializer())
    mapper.registerModule(module)
}

The method wasn’t called, however. But it’s annotated! Well, it’s the wrong annotation if you’re using JUnit 5. The correct one is @BeforeEach. This one and @BeforeClass (new name @BeforeAll) have been changed from version 4 to 5 to make their meaning more obvious.

But that’s besides the point. The question is: where does this @Before come from then?

A look at the dependency tree quickly reveals the culprit.

It’s the official JetBrains Kotlin JUnit test artifact. Although it doesn’t hurt me to have it in my project, it certainly caused some confusion and I’d like to avoid that in the future. Hence, I excluded the old version of JUnit in my POM file for this dependency.

<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-test-junit</artifactId>
    <version>${kotlin.version}</version>
    <scope>test</scope>
    <exclusions>
        <exclusion>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
        </exclusion>
    </exclusions>
</dependency>

Problem solved.

Using Groovy Spock in a Maven Java Project

Groovy Spock is a testing framework that can be used as an alternative to the venerable JUnit. In Java projects it’s probably very common (I don’t have any data, just an assumption based on how I think) to also use a Java based testing framework. The most widely known is JUnit, although not the only one of its kind (e.g. see this article on DZone). However, Java’s syntax can sometimes be rather cumbersome and verbose, and this is where a dynamic language like Groovy can help. It is often used to create nice and interesting DSLs, e.g. as the basis of the Gradle project or, as in the case of Spock, for testing.

Here’s how to integrate the Groovy Spock testing framework in a Maven based Java project.

One thing up front: I’m no fan of Groovy. I’ve worked with Grails projects for several years and using Groovy has more than once proven to be a problem. Especially in very large applications. However, I do see the benefits it can provide in certain situations and I have come to like the more expressive, although sometimes odd to read, Spock DSL in tests.

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