How to Mock in Integration Tests - Junit

Question

Im doing integration tests and one of my service is using firebase call to save the data. I want to mock the internal method call that uses the firebase call to indirectly mock the firebase.

public class EventFactory {

private static final EnumMap<EventType, EventCommand> command = new EnumMap<>(EventType.class);

public EventFactory(List<EventCommand> cms) {
    cms.forEach(c -> command.put(c.getType(), c));
}

public static EventCommand getEvent(EventType eventType) {
    EventCommand eventCommand = command.get(eventType);
    if (ObjectUtils.isEmpty(eventCommand)) return null;
    return eventCommand;
}

}

I have the handler as,

public class AppEventListener {

@TransactionalEventListener(phase = TransactionPhase.AFTER_COMMIT)
public void handle(Event event) {

    EventCommand command = EventFactory.getEvent(event.getEventType());
    if (!ObjectUtils.isEmpty(command)) {
        command.execute(event);
    } else{
        log.error("No Command Found For Provided Event");
    }
}
}

I have my CommandService as follows,

public class CommandService implements EventCommand{

private final RealTimeDbService realTime;

public CommandService(RealTimeDbService realTime) {
    this.realTime = realTime;
}

@Override
public void execute(Event event) {
    MyEvent ev = (MyEvent) event;

    log.info("Saving To Firebase");
    realTime.save(ev.getDocument());
}
}

My RealTimeDbService is as follows,

public class RealTimeDbService {

public void saveDocument(MyDocument myDoc) {
    DocumentReference docRef = getCollection("col").document("myKey");
    docRef.get().get();
    docRef.set(myDoc);
}

public CollectionReference getCollection(String name) {
    return FirestoreClient.getFirestore().collection(name);
}
}

Here I want to mock getCollection method to avoid Firebase hit and return some dummy CollectionReference

My Test is as follows

@SpringBootTest(webEnvironment = 
SpringBootTest.WebEnvironment.RANDOM_PORT)
@ActiveProfiles("test")
@Import(TestingConfig.class)
class MyTest{

@Mock private CollectionReference collectionReference;

@Autowired
private AppEventListener appEventListener;

@Spy
private RealTimeDbService realTime;

@Test
void create() {
    MyDocument myDoc = createDoc();
    Event ev = createEvent()

    doReturn(collectionReference).when(realTime).getCollection("col");

    appEventListener.handle(ev);
}
}

The problem is the internal method is not mocked, it is getting called and reaching to firebase. How can I avoid it.