improve ChangeStream cursor test to assert cursor id is unchanged

Author: jmoghisi

test-common/src/main/java/de/bwaldvogel/mongo/backend/AbstractOplogTest.java

@@ -243,13 +243,20 @@ public void testChangeStreamInsertAndUpdateFullDocumentLookup() {
         try (MongoChangeStreamCursor<ChangeStreamDocument<Document>> cursor =
                  collection.watch(pipeline).fullDocument(FullDocument.UPDATE_LOOKUP).cursor()) {
 
+            final long cursorId = cursor.getServerCursor().getId();
+
             for (int i = 1; i < numberOfDocs + 1; i++) {
                 Document doc = json(String.format("a: %d, b: 1", i));
                 collection.insertOne(doc);
                 collection.updateOne(eq("a", i), set("c", i * 10));
 
+                assertThat(cursor.hasNext()).isTrue();
                 ChangeStreamDocument<Document> insertDocument = cursor.next();
+                assertThat(cursor.getServerCursor().getId()).isEqualTo(cursorId);
+
+                assertThat(cursor.hasNext()).isTrue();
                 ChangeStreamDocument<Document> updateDocument = cursor.next();
+                assertThat(cursor.getServerCursor().getId()).isEqualTo(cursorId);
 
                 assertThat(insertDocument.getFullDocument().get("a")).isEqualTo(i);
                 insert.add(insertDocument.getFullDocument());