In gradle, how to copy a subset of compiled test classes - gradle

Question

I tried taking a portion of the compiled test classes of a Gradle project, and put them in a jar file (to create a test case). What happened was, only those classes got compiled out of all test classes. Any idea how to do it right?
Here's my build.gradle:
plugins {
id 'java'
}
group 'org.example'
version '1.0-SNAPSHOT'
repositories {
mavenCentral()
}
dependencies {
testCompile group: 'junit', name: 'junit', version: '4.12'
}
task testSampleJar(type: Zip) {
archiveName "sample.jar"
from compileTestJava {
include "org/example/samples/**"
}
}
test {
dependsOn(testSampleJar)
}
So what seems to be happening is that by just defining the testSampleJar task, the compileTestJava task gets modified to only compile under org.example.samples package. My intent was to use the outputs of compileTestJava and pick something out of them them.
Thanks,
Uri

Answer 1

OK, figured it out, so the two possible solutions are:
//a global filter
task testSampleJar(type: Zip) {
archiveName "sample.jar"
from compileTestJava
include "org/example/samples/**"
}
Or
//Child specification - notice the parentheses around compileTestJava
task testSampleJar(type: Zip) {
archiveName "sample.jar"
from (compileTestJava) {
include "org/example/samples/**"
}
}
I guess the original code was defining compileTestJava instead of using its output, but I don't have a full grasp of Groovy/Gradle DSL to be certain.