Creating a Custom ShadowJar Task

The built in shadowJar task only provides an output for the main source set of the project. It is possible to add arbitrary ShadowJar tasks to a project. When doing so, ensure that the configurations property is specified to inform Shadow which dependencies to merge into the output.

// Shadowing Test Sources and Dependencies
import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar

task testJar(type: ShadowJar) {
  archiveClassifier.set("tests")
  from sourceSets.test.output
  configurations = [project.configurations.testImplementation]
}

The code snippet above will generate a shadowed JAR containing both the main and test sources as well as all runtime and testImplementation dependencies. The file is output to build/libs/<project>-<version>-tests.jar.