Multi-JVM testing for Gradle

This plugin automatically configures a Java (or Kotlin, or other plugins applying Java) build to run tests under multiple versions of the JVM. It exposes support to decide on which JVM to compile code, pre-configures the test task to run on the same JVM, and creates the following additional tasks:

• testWithJvmXXX, where XXX is the version of a supported JVM, e.g., 16, one such task is created for each version of the JVM that the project supports;
• testWithLatestJvm, that runs tests with the latest known JVM;
• testWithLtsJvms, that runs tests with all the known LTS versions of the JVM;
• testWithLtsAndLatestJvms, that runs both testWithLatestJvm and testWithLtsJvms

A set of all tasks can be selected in configuration, and will be associated to the check task for being run by default. If there is only one task of type test, it will be preconfigured to use the same JVM used for compiling code.

Configuration

To provision the missing JVMs automatically, you should enable org.gradle.toolchains.foojay-resolver-convention in your settings.gradle.kts:

plugins {
    id("org.gradle.toolchains.foojay-resolver-convention") version "<LATEST VERSION IS RECOMMENDED>"
}

By default, the plugin compiles with Java 8, and tests with all the LTS versions from Java 8 onwards, plus with the most recent Java version.

This behaviour can be changed as follows in your build.gradle.kts:

plugins {
    id("org.danilopianini.multi-jvm-test-plugin") version "<VERSION_YOU_WANT>" 
}

multiJvm {
    jvmVersionForCompilation.set(8) // Select the version you want to compile with
    maximumSupportedJvmVersion.set(latestJava) // Select the latest version of the JVM you intend to support
    excludeSupportFor(10) // It is possible to exclude one or more versions from the set of supported JVMs
    println(latestJava) // latestJava returns the newest known version of Java
    println(allLtsVersions) // allLtsVersions returns all the known LTS versions of Java
    println(latestJavaSupportedByGradle) // latestJavaSupportedByGradle is the latest Java version supported by the running version of Gradle
    testByDefaultWith(supportedLtsVersionsAndLatest) // this method can be called with other parameters to change wich JVMs should be used by default for tests
}

Beware of configuration avoidance

This plugin uses Gradle's configuration avoidance API to improve performance. A con of this approach is that the plugin expects the task configuration to be done using the same api. In particular, configurations like this one will fail:

// THIS IS BROKEN, DO NOT DO THIS
tasks.withType<Test> {
    useJUnitPlatform()
}
// IT IS BROKEN, DON'T COPY AND PASTE THIS CODE WITHOUT READING THE COMMENT ABOVE
multiJvm {
    jvmVersionForCompilation.set(latestJavaSupportedByGradle)
    maximumSupportedJvmVersion.set(latestJavaSupportedByGradle)
}

As gradle will run the task configuration for Test tasks before the plugin's extension has been configured. To solve, there are two options:

1. configure the extension before any other task configuration;
2. use the configuration avoidance API to configure the tasks.

The two things are not mutually exclusive, rather, it is recommended to do both:

multiJvm {
    jvmVersionForCompilation.set(latestJavaSupportedByGradle)
    maximumSupportedJvmVersion.set(latestJavaSupportedByGradle)
}
tasks.withType<Test>().configureEach {
    useJUnitPlatform()
}