I want to have a Gradle task that runs tests for my library using a specific JRE (8, the oldest one ...

# gradle

[Piotr Krzemiński]

I want to have a Gradle task that runs tests for my library using a specific JRE (8, the oldest one I want to support). Looking at toolchains for tasks, it should be fairly simple, but it's giving me this in runtime:

Cannot invoke "org.gradle.api.file.FileCollection.getAsFileTree()" because the return value of "org.gradle.api.tasks.testing.Test.getTestClassesDirs()" is null

How can I fix it?
CC @Adam S

[tapchicoma]

Could you post the full stracktrace?

[Piotr Krzemiński]

https://pastebin.com/Yq7N02rS

[tapchicoma]

Could you show how you configure the task?

[Piotr Krzemiński]

after this curly brace, I put the snippet from the docs, but replaced 17 with 8:

tasks.register<Test>("testsOn8") {
    javaLauncher = javaToolchains.launcherFor {
        languageVersion = JavaLanguageVersion.of(8)
    }
}

[Adam S]

For KMP try this instead:

kotlin {
    targets.withType<KotlinJvmTarget>().configureEach {
        testRuns.register("${name}_testJdk8") {
            executionTask.configure {
                javaLauncher = javaToolchains.launcherFor {
                    languageVersion = JavaLanguageVersion.of(8)
                }
            }
        }
    }
}

[Piotr Krzemiński]

@Adam S Could not create domain object 'jvm_testJdk8' (KotlinJvmTestRun) 🤔
at the very bottom of the stack trace:

Caused by: java.lang.NullPointerException: Cannot invoke "org.gradle.api.file.FileCollection.getFiles()" because "files" is null

[Piotr Krzemiński]

I'll push it to PR so that you have context of the whole code base

[tapchicoma]

do you need it in KMP project or JVM only?

[Piotr Krzemiński]

KMP, it's for snakeyaml-engine-kmp

See the PR with the change proposed by Adam, where CI will probably fail in a minute: https://github.com/krzema12/snakeyaml-engine-kmp/pull/203 (or if it doesn't fail, it means something's wrong with my local setup)

[tapchicoma]

Something like this should work for Kotlin/JVM:

tasks.register<Test>("testsOn8") {
    classpath = sourceSets.test.get().runtimeClasspath
    testClassesDirs = sourceSets.test.get().output.classesDirs
    workingDir = projectDir
    javaLauncher = javaToolchains.launcherFor {
        languageVersion = JavaLanguageVersion.of(8)
    }
    useJUnitPlatform()
}

[tapchicoma]

probably you need to adapt @Adam Semenenko approach here with mine