Reference Kotlin pom

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<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/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>foobar</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <!-- https://stackoverflow.com/a/3018152/245602 -->

        <java.version>11</java.version> <!-- Also picked up by Spring. -->
        <maven.compiler.source>${java.version}</maven.compiler.source>
        <maven.compiler.target>${java.version}</maven.compiler.target>
        <kotlin.compiler.jvmTarget>${java.version}</kotlin.compiler.jvmTarget>

        <kotlin.version>1.4.32</kotlin.version>
        <kotlin.code.style>official</kotlin.code.style>

        <junit-jupiter.version>5.7.1</junit-jupiter.version>
        <logback.version>1.2.3</logback.version>
        <surefire.version>2.22.2</surefire.version>
        <maven-compiler.version>3.8.1</maven-compiler.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib-jdk8</artifactId>
            <version>${kotlin.version}</version>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-test-junit5</artifactId>
            <version>${kotlin.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>${logback.version}</version>
            <optional>true</optional> <!-- Don't force on downstream projects. -->
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.junit</groupId>
                <artifactId>junit-bom</artifactId>
                <version>${junit-jupiter.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>${surefire.version}</version>
            </plugin>
            <plugin>
                <groupId>org.jetbrains.kotlin</groupId>
                <artifactId>kotlin-maven-plugin</artifactId>
                <version>${kotlin.version}</version>
                <configuration>
                    <args>
                        <arg>-Xjvm-default=enable</arg> <!-- https://kotlinlang.org/docs/java-to-kotlin-interop.html#default-methods-in-interfaces -->
                        <arg>-Xjsr305=strict</arg> <!-- https://kotlinlang.org/docs/java-interop.html#jsr-305-support -->
                    </args>
                </configuration>
                <executions>
                    <execution>
                        <id>compile</id>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                        <configuration>
                            <sourceDirs>
                                <sourceDir>${project.basedir}/src/main/kotlin</sourceDir>
                                <sourceDir>${project.basedir}/src/main/java</sourceDir>
                            </sourceDirs>
                        </configuration>
                    </execution>
                    <execution>
                        <id>test-compile</id>
                        <goals>
                            <goal>test-compile</goal>
                        </goals>
                        <configuration>
                            <sourceDirs>
                                <sourceDir>${project.basedir}/src/test/kotlin</sourceDir>
                                <sourceDir>${project.basedir}/src/test/java</sourceDir>
                            </sourceDirs>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>${maven-compiler.version}</version>
                <configuration>
                    <compilerArgs>
                        <!-- https://docs.oracle.com/en/java/javase/14/docs/specs/man/javac.html -->
                        <arg>-Xlint:unchecked</arg>
                    </compilerArgs>
                </configuration>
                <executions>
                    <!-- Replacing default-compile as it is treated specially by maven -->
                    <execution>
                        <id>default-compile</id>
                        <phase>none</phase>
                    </execution>
                    <!-- Replacing default-testCompile as it is treated specially by maven -->
                    <execution>
                        <id>default-testCompile</id>
                        <phase>none</phase>
                    </execution>
                    <execution>
                        <id>java-compile</id>
                        <phase>compile</phase>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>java-test-compile</id>
                        <phase>test-compile</phase>
                        <goals>
                            <goal>testCompile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

I added the junit-bom in the dependencyManagement section despite just having just onedirect JUnit dependency whose version tag could be dropped as a result. This resolved very odd failures when running mvn test (the Surefire plugin would exit with strange exceptions that seemed to be the result of NoClassDefFoundError). You can get more informative output from Maven with:

$ mvn -DforkMode=never -e clean test

I tried various things to resolve this, including many of the suggestion in this SO answer, but in the end it was adding the junit-bom block that did the trick.

I also added maven-surefire-plugin to the plugins section so I could make sure that the latest version of the plugin is used. If I was using the spring-boot-starter-parent parent pom, I don't think this would be necessary (and perhaps also the junit-bom would be unnecessary too).