How to create a custom task in gradle to pack java and kotlin code to a jar?

Question

We have a multi modular setup and we are sharing some tests classes between the modules (mainly Fakes implementations). Our current solution (that you can find below) works just for classes written in Java, but we are looking at supporting also shared kotlin classes.

if (isAndroidLibrary()) {
    task compileTestCommonJar(type: JavaCompile) {
        classpath = compileDebugUnitTestJavaWithJavac.classpath
        source sourceSets.testShared.java.srcDirs
        destinationDir = file('build/testCommon')
    }
    taskToDependOn = compileDebugUnitTestSources
} else {
    task compileTestCommonJar(type: JavaCompile) {
        classpath = compileTestJava.classpath
        source sourceSets.testShared.java.srcDirs
        destinationDir = file('build/testCommon')
    }
    taskToDependOn = testClasses
}

task testJar(type: Jar, dependsOn: taskToDependOn) {
    classifier = 'tests'
    from compileTestCommonJar.outputs
}

How can I modify the compileTestCommonJar so it supports kotlin?

Answer 1

Here is what we do:

1. In the module with shared test classes, pack the test source set output into a jar

configurations { tests }
...
task testJar(type: Jar, dependsOn: testClasses) {
    baseName = "test-${project.archivesBaseName}"
    from sourceSets.test.output
}

artifacts { tests testJar }

2. In a module that depends on the shared classes

dependencies {
  testCompile project(path: ":my-project-with-shared-test-classes", configuration: "tests")
}

PS: Honestly, I would prefer to have a separate Gradle module with common test classes as it's more explicit solution.