Make ReactiveDefaultBookmarkManager return a copy of bookmarks

src/main/java/org/springframework/data/neo4j/core/transaction/ReactiveDefaultBookmarkManager.java

@@ -29,6 +29,7 @@
  * Default bookmark manager.
  *
  * @author Michael J. Simons
+ * @author Dmitriy Tverdiakov
  * @soundtrack Helge Schneider - The Last Jazz
  * @since 7.0
  */
@@ -48,7 +49,7 @@ final class ReactiveDefaultBookmarkManager extends AbstractBookmarkManager {
 @Override
 public Collection<Bookmark> getBookmarks() {
 this.bookmarks.addAll(bookmarksSupplier.get());
-return Collections.synchronizedSet(Collections.unmodifiableSet(this.bookmarks));
+return Collections.synchronizedSet(Collections.unmodifiableSet(new HashSet<>(this.bookmarks)));
 }
 
 @Override

src/test/java/org/springframework/data/neo4j/core/transaction/ReactiveDefaultBookmarkManagerTest.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2011-2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.neo4j.core.transaction;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.junit.jupiter.api.Test;
+import org.neo4j.driver.Bookmark;
+
+/**
+ * @author Dmitriy Tverdiakov
+ */
+class ReactiveDefaultBookmarkManagerTest {
+@Test
+void shouldReturnBookmarksCopy() {
+var manager = new ReactiveDefaultBookmarkManager(null);
+var initialBookmarks = new HashSet<>(Arrays.asList(Bookmark.from("bookmark 1"), null));
+manager.updateBookmarks(Collections.emptyList(), initialBookmarks);
+
+var bookmarks = manager.getBookmarks();
+manager.updateBookmarks(initialBookmarks, Set.of(Bookmark.from("bookmark2")));
+
+assertEquals(initialBookmarks, bookmarks);
+}
+
+@Test
+void shouldReturnUnmodifiableBookmarks() {
+var manager = new ReactiveDefaultBookmarkManager(null);
+var initialBookmarks = Set.of(Bookmark.from("bookmark1"));
+manager.updateBookmarks(Collections.emptyList(), initialBookmarks);
+var bookmarks = manager.getBookmarks();
+
+assertThrows(UnsupportedOperationException.class, () -> bookmarks.add(Bookmark.from("bookmark 2")));
+assertThrows(UnsupportedOperationException.class, () -> bookmarks.remove(Bookmark.from("bookmark 1")));
+assertThrows(UnsupportedOperationException.class, bookmarks::clear);
+}
+}