sourceSets example complete with extendsFrom for configuration and compileClasspath inheritance

[hmarggraff]

I have not found a way to translate the groovy definition of a source Set for integration tests into the Kotlin DSL.

What I want:

1. Place integration tests in a separate source directory src/itest/kotlin
2. Make the classes from main sourceSet visible there via compileClasspath/runtimeClasspath
3. Add a specific dependency for the integration tests
4. Create a task that runs the integration tests

The groovy example is taken from here: https://www.petrikainulainen.net/programming/gradle/getting-started-with-gradle-integration-testing/

Groovy:
sourceSets {
integrationTest {
java {
compileClasspath += main.output + test.output
runtimeClasspath += main.output + test.output
srcDir file('src/integration-test/java')
}
resources.srcDir file('src/integration-test/resources')
}
}
configurations {
integrationTestCompile.extendsFrom testCompile
integrationTestRuntime.extendsFrom testRuntime
}
dependencies {
compile 'log4j:log4j:1.2.17'
testCompile 'junit:junit:4.11'
integrationTestCompile 'org.assertj:assertj-core:3.0.0'
}
task integrationTest(type: Test) {
testClassesDirs = sourceSets.integrationTest.output.classesDirs
classpath = sourceSets.integrationTest.runtimeClasspath
outputs.upToDateWhen { false }
}