Custom SourceSet for exposing TestBuilders through a shared-test jar using Gradle

a-services-api-build.gradle

dependencies {
  // a-services-api dependencies, if any
}

sourceSets {
    sharedTest {
        java {
            compileClasspath += sourceSets.main.runtimeClasspath
            srcDirs 'src/sharedTest/java'
        }
    }
}

compileJava {
    doLast {
        compileSharedTestJava
    }
}

task sharedTestJar(type: Jar, dependsOn: compileSharedTestJava) {
    from sourceSets.sharedTest.output
    classifier = 'shared-test'
}

configurations {
    sharedTestCompile.extendsFrom compile //might not be necessary
    sharedTestProvided.extendsFrom provided //might not be necessary
    sharedTest
}

artifacts {
    sharedTest sharedTestJar
}

jar {
    dependsOn {
        sharedTestJar
    }
}

b-services-impl-build.gradle

dependencies {
  // other compile dependencies...
  testCompile project(path:':a-services-api', configuration: 'sharedTest')
}

SharedTestSourceSet.md

#Context We have a project set-up of:

project-A
  a-services-api
  a-services-impl
project-B
  b-services-api
  b-services-impl
non-gradle-project-C

a-services-impl depends on a-services-api through project dependency. b-services-impl also depends on a-services-api through project dependency. non-gradle-project-C also depends on a-services-api through jar dependency.

#Problem a-services-api contains a class that we wish to only be instantiatable in a-services-impl and nowhere else. But we want to be able to do so within the tests of b-services-impl. So, TestBuilder pattern to the rescue!

project-A
  a-services-api
    src/main/java/be/swsb/example/ExampleTO.java --> has package/default protected constructor
    src/sharedTest/java/be/swsb/example/ExampleTestBuilder.java
  a-services-impl
    src/main/java/be/swsb/example/ExampleTOFactory.java (or ExampleTOBuilder.java)
project-B
  b-services-impl
    src/main/java/be/swsb/exampleusage/UsesExampleInterface.java
    src/main/test/be/swsb/exampleusage/UsesExampleInterfaceTest.java --> needs to be able to instantiate (and not Mock!!!) an ExampleTO
non-gradle-project-C
  same config as project-B really

Note that we created our own SourceSet called sharedTest. Because we think making a separate SourceSet is clearer than filtering *TestBuilder.java within the default src/test/java SourceSet.