Introduce isClosed() in NamespacedHierarchicalStore

Closes #3807

junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStore.java

@@ -84,6 +84,18 @@ public NamespacedHierarchicalStore<N> newChild() {
 		return new NamespacedHierarchicalStore<>(this, this.closeAction);
 	}
 
+	/**
+	 * Determine if this store has been {@linkplain #close() closed}.
+	 *
+	 * @return {@code true} if this store has been closed
+	 * @since 1.11
+	 * @see #close()
+	 */
+	@API(status = EXPERIMENTAL, since = "1.11")
+	public boolean isClosed() {
+		return this.closed;
+	}
+
 	/**
 	 * If a close action is configured, it will be called with all successfully
 	 * stored values in reverse insertion order.
@@ -92,6 +104,8 @@ public NamespacedHierarchicalStore<N> newChild() {
 	 *
 	 * <p>Invocations of this method after the store has already been closed will
 	 * be ignored.
+	 *
+	 * @see #isClosed()
 	 */
 	@Override
 	public void close() {

platform-tests/src/test/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStoreTests.java

@@ -28,6 +28,7 @@
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Function;
 
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 
@@ -371,6 +372,11 @@ void additionNamespacePartMakesADifference() {
 	@Nested
 	class CloseActionTests {
 
+		@BeforeEach
+		void prerequisites() {
+			assertNotClosed();
+		}
+
 		@Test
 		void callsCloseActionInReverseInsertionOrderWhenClosingStore() throws Throwable {
 			store.put(namespace, "key1", "value1");
@@ -379,6 +385,8 @@ void callsCloseActionInReverseInsertionOrderWhenClosingStore() throws Throwable
 			verifyNoInteractions(closeAction);
 
 			store.close();
+			assertClosed();
+
 			var inOrder = inOrder(closeAction);
 			inOrder.verify(closeAction).close(namespace, "key3", "value3");
 			inOrder.verify(closeAction).close(namespace, "key2", "value2");
@@ -391,6 +399,7 @@ void doesNotCallCloseActionForRemovedValues() {
 			store.remove(namespace, key);
 
 			store.close();
+			assertClosed();
 
 			verifyNoInteractions(closeAction);
 		}
@@ -401,6 +410,7 @@ void doesNotCallCloseActionForReplacedValues() throws Throwable {
 			store.put(namespace, key, "value2");
 
 			store.close();
+			assertClosed();
 
 			verify(closeAction).close(namespace, key, "value2");
 			verifyNoMoreInteractions(closeAction);
@@ -411,6 +421,7 @@ void doesNotCallCloseActionForNullValues() {
 			store.put(namespace, key, null);
 
 			store.close();
+			assertClosed();
 
 			verifyNoInteractions(closeAction);
 		}
@@ -422,6 +433,7 @@ void ignoresStoredValuesThatThrewExceptionsDuringCleanup() {
 			}));
 
 			assertDoesNotThrow(store::close);
+			assertClosed();
 
 			verifyNoInteractions(closeAction);
 		}
@@ -433,6 +445,8 @@ void doesNotIgnoreStoredValuesThatThrewUnrecoverableFailuresDuringCleanup() {
 			}));
 
 			assertThrows(OutOfMemoryError.class, store::close);
+			// TODO Reinstate assertion once we ensure the store is closed even if an exception is thrown.
+			// assertClosed();
 
 			verifyNoInteractions(closeAction);
 		}
@@ -444,17 +458,20 @@ void closeIsIdempotent() throws Throwable {
 			verifyNoInteractions(closeAction);
 
 			store.close();
+			assertClosed();
 
 			verify(closeAction, times(1)).close(namespace, "key1", "value1");
 
 			store.close();
+			assertClosed();
 
 			verifyNoMoreInteractions(closeAction);
 		}
 
 		@Test
 		void rejectsModificationAfterClose() {
 			store.close();
+			assertClosed();
 
 			assertThrows(IllegalStateException.class, () -> store.put(namespace, "key1", "value1"));
 			assertThrows(IllegalStateException.class, () -> store.remove(namespace, "key1"));
@@ -464,6 +481,7 @@ void rejectsModificationAfterClose() {
 		@Test
 		void rejectsQueryAfterClose() {
 			store.close();
+			assertClosed();
 
 			assertThrows(IllegalStateException.class, () -> store.get(namespace, "key1"));
 			assertThrows(IllegalStateException.class, () -> store.get(namespace, "key1", Integer.class));
@@ -472,6 +490,15 @@ void rejectsQueryAfterClose() {
 			assertThrows(IllegalStateException.class,
 				() -> store.getOrComputeIfAbsent(namespace, "key1", k -> 1337, Integer.class));
 		}
+
+		private void assertNotClosed() {
+			assertThat(store.isClosed()).as("closed").isFalse();
+		}
+
+		private void assertClosed() {
+			assertThat(store.isClosed()).as("closed").isTrue();
+		}
+
 	}
 
 	private static Object createObject(String display) {