Add test for WorkerLeaseManager and WorkerLease

Author: marcphilipp

junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ConcurrentHierarchicalTestExecutorService.java

@@ -72,7 +72,7 @@ public ConcurrentHierarchicalTestExecutorService(ParallelExecutionConfiguration
 		threadPool = new ThreadPoolExecutor(configuration.getCorePoolSize(), configuration.getMaxPoolSize(),
 			configuration.getKeepAliveSeconds(), SECONDS, new SynchronousQueue<>(), threadFactory);
 		parallelism = configuration.getParallelism();
-		workerLeaseManager = new WorkerLeaseManager(parallelism);
+		workerLeaseManager = new WorkerLeaseManager(parallelism, this::maybeStartWorker);
 		LOGGER.trace(() -> "initialized thread pool for parallelism of " + configuration.getParallelism());
 	}
 
@@ -554,12 +554,14 @@ private boolean isContainer() {
 
 	}
 
-	private class WorkerLeaseManager {
+	static class WorkerLeaseManager {
 
 		private final Semaphore semaphore;
+		private final Runnable onRelease;
 
-		WorkerLeaseManager(int parallelism) {
-			semaphore = new Semaphore(parallelism);
+		WorkerLeaseManager(int parallelism, Runnable onRelease) {
+			this.semaphore = new Semaphore(parallelism);
+			this.onRelease = onRelease;
 		}
 
 		@Nullable
@@ -575,7 +577,7 @@ WorkerLease tryAcquire() {
 		private ReacquisitionToken release() {
 			semaphore.release();
 			LOGGER.trace(() -> "release worker lease (available: %d)".formatted(semaphore.availablePermits()));
-			maybeStartWorker();
+			onRelease.run();
 			return new ReacquisitionToken();
 		}
 
@@ -596,7 +598,7 @@ void reacquire() throws InterruptedException {
 		}
 	}
 
-	private static class WorkerLease implements AutoCloseable {
+	static class WorkerLease implements AutoCloseable {
 
 		private final Supplier<WorkerLeaseManager.ReacquisitionToken> releaseAction;
 		private WorkerLeaseManager.@Nullable ReacquisitionToken reacquisitionToken;

platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/WorkerLeaseManagerTests.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.engine.support.hierarchical;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.junit.jupiter.api.Test;
+import org.junit.platform.engine.support.hierarchical.ConcurrentHierarchicalTestExecutorService.WorkerLeaseManager;
+
+class WorkerLeaseManagerTests {
+
+	@Test
+	void releasingIsIdempotent() {
+		var released = new AtomicInteger();
+		var manager = new WorkerLeaseManager(1, released::incrementAndGet);
+
+		var lease = manager.tryAcquire();
+		assertThat(lease).isNotNull();
+
+		lease.close();
+		assertThat(released.get()).isEqualTo(1);
+
+		lease.close();
+		assertThat(released.get()).isEqualTo(1);
+	}
+
+	@Test
+	void leaseCanBeReacquired() throws Exception {
+		var released = new AtomicInteger();
+		var manager = new WorkerLeaseManager(1, released::incrementAndGet);
+
+		var lease = manager.tryAcquire();
+		assertThat(lease).isNotNull();
+
+		lease.close();
+		assertThat(released.get()).isEqualTo(1);
+
+		lease.reacquire();
+		assertThat(released.get()).isEqualTo(1);
+
+		lease.close();
+		assertThat(released.get()).isEqualTo(2);
+	}
+}