Geb, Spock, Gradle and maxParallelForks - selenium

Question

I am having some trouble understanding an issue we are having with our Geb/Spock tests. We are using gradle and we are trying to run our tests in parallel. As I understand it, the maxParallelForks property in gradle will run test classes in separate JVMs.
The issue I am running into is when I have 6 test classes and I set maxParallelForks to 4, when the test starts I will get 4 test classes running in parallel. Awesome! But the final 2 classes is where the problem is. Let's say out of the first 4 classes running, 2 of the classes are done in 1 minute and 2 of the classes are done in 5 minutes. What I'm seeing is instead of the first 2 finishing and starting the next 2 classes, it seems to waiting until the last 2 long running classes finish before spinning up the other forks. This is way less than ideal.
Am I misunderstanding something or am I missing a property somewhere? This is what I have in my build.gradle:
tasks.withType(Test) {
systemProperties System.properties
maxParallelForks = 4
forkEvery = 1
}

Answer 1

Classes are assigned to forks for execution upfront and not on a polling basis. So the first two forks will get two classes assigned upfront and the other two one each regardless of how long each of these classes takes to finish. In worst case scenario two of the longest running classes will be assigned to the a single fork. This is how it works - classes are split into groups and then separate test jvms (forks) are spun up with the list of classes to execute for each of them.
On a side note - you don't want to do forkEvery = 1 - this will restart your test jvms after each test class slowing your test execution down for no benefit.

Answer 2

Using JUNIT suites you can decide which set of classes need to be picked by a particular fork.
import org.junit.runner.RunWith
import org.junit.runners.Suite
#RunWith(Suite.class)
#Suite.SuiteClasses([
TimeTaking.class, // Class that takes a lot of time
NotSoMuchTimeTaking.class, //Class that is quick
// Add more test classes which need to be executed in same fork.
])
public class FirstTestSuite { // keep this empty
}
Similarly, create a SecondTestSuite {
} and so on..
In addition to above steps, include the *TestSuite.class in your build.gradle
tasks.withType(Test) {
systemProperties System.properties
maxParallelForks = 4
forkEvery = 1
include '**/*TestSuite*.class'
}
This way, you will be able to control your execution and decide which test classes need to be executed in what order.