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 (opens new window) 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
def testShadowJar = tasks.register('testShadowJar', com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar) {
  group = com.github.jengelman.gradle.plugins.shadow.ShadowBasePlugin.GROUP_NAME
  description = "Create a combined JAR of project and test dependencies"
  
  archiveClassifier = "tests"
  from sourceSets.test.output
  configurations = [project.configurations.testRuntimeClasspath]
}

// Optionally, make the `assemble` task depend on the new task
tasks.named('assemble') {
  dependsOn testShadowJar
}

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