How to mock mongodb connection for testing using Mockito in Springboot?

I'm new to testing framework I have to test a function which have involves storing data from Db into list.

Note: I don't have any POJO Class or Entity class for this.

I'm just connecting to the database. Following is the method for which I want to write test cases. I have basic knowledge about Junit and Mockito. I know if we have MongoRepository or template then we can use the @Mock annotation and can mock the repo which we have created. But in my case I don't know how I should mock the DB.

Following is the function --

public List<FriendDetails> fetchStationIds() {
        AtomicInteger count = new AtomicInteger();
        List<FriendDetails> list = new ArrayList<>();
        MongoDatabase database = mongoClient.getDatabase("Friends");
        MongoCollection<Document> collection = database.getCollection("Friend");
        BasicDBObject filter = new BasicDBObject("$and", Arrays.asList(new BasicDBObject("name", new BasicDBObject("$regex", "^Ram")).append("id", new BasicDBObject("$regex", "Shyam$"))));
        collection.find(filter).forEach((Consumer<Document>) doc -> {
            count.getAndIncrement();
            String name = (String) doc.get("name");
                if(name != null) {
                    String nameSpace = name.substring(0, name.indexOf("a") + 1);
                    String temp = name.substring(name.indexOf("a") + 1);
                    Document FriendValue1 = ((ArrayList<Document>) doc.get("Main_array")).get(0);
                    ArrayList<Document> arrayList = (ArrayList<Document>) FriendValue1.get("Main_ArrayPart2");
                    if(!arrayList.isEmpty()) {
                        Document FriendValue2 = arrayList.get(0);

                        Long number = (Long) FriendValue2.get("number");
                        String pinCode = (String) FriendValue2.get("pincode");
                        FriendDetails friendDetail = new FriendDetails(nameSpace, temp, number, pincode);
                        if (listDoesNotContain(list, friendDetail.toString())) {
                            list.add(friendDetail);
                        }
                    }
                }
        });
        return list;

    }

Test case I tried to write --

@Mock
    private MongoClient mockClient;
    @Mock
    private MongoCollection mockCollection;
    @Mock
    private MongoDatabase mockDB;

    @InjectMocks
    private FriendsDetails wrapper;

    @Before
    public void initMocks() {
        when(mockClient.getDatabase(anyString())).thenReturn(mockDB);
        when(mockDB.getCollection(anyString())).thenReturn(mockCollection);
        wrapper.initName();
        MockitoAnnotations.initMocks(this);
    }
   
        @Test
        void testFetch(){
      
            FindIterable iterable = mock(FindIterable.class); //which class I should mock
            MongoCursor cursor = mock(MongoCursor.class);
            Document bob = new Document("_id",new ObjectId("579397d20c2dd41b9a8a09eb"))
                    .append("firstName", "Bob")
                    .append("lastName", "Bobberson")
                     .append("number","36273872")
                     .append("pincode", "677");

            when(mockCollection.find()))
                    .thenReturn());

            assertEquals(expected, actual));
        }
    }