Introduce default semantics for Node.isLeaf()

junit-engine-api/src/main/java/org/junit/gen5/engine/support/hierarchical/HierarchicalTestExecutor.java

@@ -78,11 +78,15 @@ private void execute(TestDescriptor testDescriptor, C parentContext) {
 			C context = node.before(preparedContext);
 			context = node.execute(context);
 
-			if (!node.isLeaf()) { // Prevent execution of dynamically added children
+			// If a node is not a leaf, execute its children recursively.
+			// Note: executing children for a leaf would result in accidental
+			// execution of dynamically added children.
+			if (!node.isLeaf()) {
 				for (TestDescriptor child : testDescriptor.getChildren()) {
 					execute(child, context);
 				}
 			}
+
 			node.after(context);
 		});
 
@@ -96,11 +100,6 @@ private Node<C> asNode(TestDescriptor testDescriptor) {
 
 	@SuppressWarnings("rawtypes")
 	private static final Node noOpNode = new Node() {
-
-		@Override
-		public boolean isLeaf() {
-			return true;
-		}
 	};
 
 }

junit-engine-api/src/main/java/org/junit/gen5/engine/support/hierarchical/Node.java

@@ -29,8 +29,12 @@ public interface Node<C extends EngineExecutionContext> {
 
 	/**
 	 * Determine if this {@code Node} is a leaf in the hierarchy.
+	 *
+	 * <p>The default implementation returns {@code false}.
 	 */
-	boolean isLeaf();
+	default boolean isLeaf() {
+		return false;
+	}
 
 	/**
 	 * Prepare the supplied {@code context} prior to execution.
@@ -54,10 +58,14 @@ default SkipResult shouldBeSkipped(C context) throws Exception {
 	/**
 	 * Execute the <em>before</em> behavior of this node.
 	 *
-	 * <p>This method will be called once <em>before</em> executing this node.
+	 * <p>This method will be called once <em>before</em> {@linkplain #execute
+	 * execution} of this node.
 	 *
 	 * @param context the context to execute in
 	 * @return the new context to be used for children of this node
+	 *
+	 * @see #execute
+	 * @see #after
 	 */
 	default C before(C context) throws Exception {
 		return context;
@@ -69,6 +77,9 @@ default C before(C context) throws Exception {
 	 * @param context the context to execute in
 	 * @return the new context to be used for children of this node and for the
 	 * <em>after</em> behavior of the parent of this node, if any
+	 *
+	 * @see #before
+	 * @see #after
 	 */
 	default C execute(C context) throws Exception {
 		return context;
@@ -77,9 +88,13 @@ default C execute(C context) throws Exception {
 	/**
 	 * Execute the <em>after</em> behavior of this node.
 	 *
-	 * <p>This method will be called once <em>after</em> executing this node.
+	 * <p>This method will be called once <em>after</em> {@linkplain #execute
+	 * execution} of this node.
 	 *
 	 * @param context the context to execute in
+	 *
+	 * @see #before
+	 * @see #execute
 	 */
 	default void after(C context) throws Exception {
 	}

junit5-engine/src/main/java/org/junit/gen5/engine/junit5/descriptor/JUnit5EngineDescriptor.java

@@ -34,9 +34,4 @@ public JUnit5EngineExecutionContext before(JUnit5EngineExecutionContext context)
 		return context.extend().withExtensionRegistry(createRegistryWithDefaultExtensions()).build();
 	}
 
-	@Override
-	public boolean isLeaf() {
-		return false;
-	}
-
 }