Introduce experimental memory cleanup mode

junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherConstants.java

@@ -269,6 +269,21 @@ public class LauncherConstants {
 	@API(status = EXPERIMENTAL, since = "6.0")
 	public static final String DISCOVERY_ISSUE_FAILURE_PHASE_PROPERTY_NAME = "junit.platform.discovery.issue.failure.phase";
 
+	/**
+	 * Property name used to enable the <em>experimental</em> memory cleanup
+	 * mode.
+	 *
+	 * <p>Supported values are {@code true} or {@code false}.
+	 *
+	 * <p>If enabled, the Launcher removes finished or skipped tests and their
+	 * children from the test plan right away to reduce memory consumption,
+	 * particularly in the presence of many dynamically reported tests.
+	 *
+	 * @since 6.1
+	 */
+	@API(status = EXPERIMENTAL, since = "6.1")
+	public static final String MEMORY_CLEANUP_ENABLED_PROPERTY_NAME = "junit.platform.execution.memory.cleanup.enabled";
+
 	private LauncherConstants() {
 		/* no-op */
 	}

junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestPlan.java

@@ -127,6 +127,14 @@ public void addInternal(TestIdentifier testIdentifier) {
 		directChildren.add(testIdentifier);
 	}
 
+	@API(status = INTERNAL, since = "6.1")
+	public void removeInternal(UniqueId uniqueId) {
+		Preconditions.notNull(uniqueId, "uniqueId must not be null");
+		allIdentifiers.remove(uniqueId);
+		roots.removeIf(testIdentifier -> testIdentifier.getUniqueIdObject().equals(uniqueId));
+		children.remove(uniqueId);
+	}
+
 	/**
 	 * Get the root {@link TestIdentifier TestIdentifiers} for this test plan.
 	 *

junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineExecutionOrchestrator.java

@@ -34,6 +34,7 @@
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.support.store.Namespace;
 import org.junit.platform.engine.support.store.NamespacedHierarchicalStore;
+import org.junit.platform.launcher.LauncherConstants;
 import org.junit.platform.launcher.TestExecutionListener;
 import org.junit.platform.launcher.TestIdentifier;
 import org.junit.platform.launcher.TestPlan;
@@ -141,11 +142,21 @@ private static EngineExecutionListener buildEngineExecutionListener(
 			EngineExecutionListener parentEngineExecutionListener, TestExecutionListener testExecutionListener,
 			TestPlan testPlan) {
 		ListenerRegistry<EngineExecutionListener> engineExecutionListenerRegistry = forEngineExecutionListeners();
-		engineExecutionListenerRegistry.add(new ExecutionListenerAdapter(testPlan, testExecutionListener));
+		EngineExecutionListener listener = new ExecutionListenerAdapter(testPlan, testExecutionListener);
+		if (isMemoryCleanupEnabled(testPlan)) {
+			listener = new MemoryCleanupListener(listener, testPlan);
+		}
+		engineExecutionListenerRegistry.add(listener);
 		engineExecutionListenerRegistry.add(parentEngineExecutionListener);
 		return engineExecutionListenerRegistry.getCompositeListener();
 	}
 
+	private static Boolean isMemoryCleanupEnabled(TestPlan testPlan) {
+		return testPlan.getConfigurationParameters() //
+				.getBoolean(LauncherConstants.MEMORY_CLEANUP_ENABLED_PROPERTY_NAME) //
+				.orElse(false);
+	}
+
 	private void withInterceptedStreams(ConfigurationParameters configurationParameters,
 			ListenerRegistry<TestExecutionListener> listenerRegistry, Consumer<TestExecutionListener> action) {
 

junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/InternalTestPlan.java

@@ -16,6 +16,7 @@
 import java.util.function.Predicate;
 
 import org.junit.platform.commons.PreconditionViolationException;
+import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.UniqueId;
 import org.junit.platform.launcher.TestIdentifier;
 import org.junit.platform.launcher.TestPlan;
@@ -61,6 +62,11 @@ public void addInternal(TestIdentifier testIdentifier) {
 		delegate.addInternal(testIdentifier);
 	}
 
+	@Override
+	public void removeInternal(UniqueId uniqueId) {
+		delegate.removeInternal(uniqueId);
+	}
+
 	@Override
 	public Set<TestIdentifier> getRoots() {
 		return delegate.getRoots();

junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/MemoryCleanupListener.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2026 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.launcher.core;
+
+import java.util.stream.Stream;
+
+import org.junit.platform.engine.EngineExecutionListener;
+import org.junit.platform.engine.TestDescriptor;
+import org.junit.platform.engine.TestExecutionResult;
+import org.junit.platform.launcher.TestPlan;
+
+/**
+ * @since 6.1
+ */
+class MemoryCleanupListener extends DelegatingEngineExecutionListener {
+
+	private final TestPlan testPlan;
+
+	MemoryCleanupListener(EngineExecutionListener delegate, TestPlan testPlan) {
+		super(delegate);
+		this.testPlan = testPlan;
+	}
+
+	@Override
+	public void executionSkipped(TestDescriptor testDescriptor, String reason) {
+		super.executionSkipped(testDescriptor, reason);
+		cleanUp(testDescriptor);
+	}
+
+	@Override
+	public void executionFinished(TestDescriptor testDescriptor, TestExecutionResult testExecutionResult) {
+		super.executionFinished(testDescriptor, testExecutionResult);
+		cleanUp(testDescriptor);
+	}
+
+	private void cleanUp(TestDescriptor testDescriptor) {
+		var ownUniqueId = Stream.of(testDescriptor.getUniqueId());
+		var descendantUniqueIds = testDescriptor.getDescendants().stream() //
+				.map(TestDescriptor::getUniqueId);
+		Stream.concat(ownUniqueId, descendantUniqueIds) //
+				.forEach(testPlan::removeInternal);
+		if (!testDescriptor.isRoot()) {
+			testDescriptor.removeFromHierarchy();
+		}
+	}
+}