Unit Testing Mongo Repositories

To test Spring Data for MongoDB, let’s use Fongo (an in-memory implementation of MongoDB meant for mocking) and Nosqlunit for MongoDB for setting up for fixtures.
Code reference: https://github.com/GlueCoders/springboot-guide/releases/tag/fongo-testingmongo

Fongo (Fake Mongo) Setup

Add pom dependency as given below.


A custom configuration class is required in test package to wire Fongo as mock MongoDB as shown below.

package org.gluecoders.library.dao.config;

import com.github.fakemongo.Fongo;
import com.mongodb.MongoClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.mongodb.config.AbstractMongoConfiguration;

public class FakeMongo extends AbstractMongoConfiguration{

    protected String getDatabaseName() {
        return "mockDB";

    public MongoClient mongo() {
        Fongo fongo = new Fongo("mockDB");
        return fongo.getMongo();


This class extends AbstractMongoConfiguration so that during Junit run, MongoTemplate and other Mongo related dependecies are taken care of automatically. In mongo() method Fongo’s instance is returned which will act as mock MongoDB.

Nosqlunit-MongoDB Setup


For nosqlunit-mongodb Junit Rule has to be wired in Test Class.

public MongoDbRule embeddedMongoDbRule = newMongoDbRule().defaultSpringMongoDb("mockDB");

Setup of DAO in test class

@Import(value = {FakeMongo.class, Database.class})
@EnableMongoRepositories(basePackageClasses = {BookDao.class})
public class BookDaoTest {

@Import imports the configuration from the given classes, in this case FakeMongo provides Fongo instance and Database provides the custom converter for YearMonth class.
@EnableMongoRepositories tells Spring to look for Mongo dependencies and enable BookDao to act as DAO layer with MongoDB as storage.

Usage of nosqlunit for fixtures

There are two basic annotations which can be used to set fixtures and assert database state after a test has run.
@UsingDataSet(locations, loadStrategy) - ensures the database has data loaded from file given in locations parameter. LoadStrategy are of three types : CLEAN_INSERT(clean and insert), DELETE_ALL(delete everything) and INSERT(append on existing data). @ShouldMatchDataSet(location) defines that data present in database should match the data given in file(location parameter). This check is done after a test case has run.

Writing unit tests

Let’s look at some of the test cases one by one.

@UsingDataSet(loadStrategy = LoadStrategyEnum.DELETE_ALL)
public void getAllBooks_NoBooks() {
   List<Book> books = bookDao.findAll();
   assertTrue("Returned book list should be empty", books.isEmpty());

This ensures that database should be clean when the test cases start, hence the test also expects that db should not return any books in the list.

@UsingDataSet(loadStrategy = LoadStrategyEnum.CLEAN_INSERT, locations = "/books/books.json")
public void getAllBooks_WithBooks() {
   List<Book> books = bookDao.findAll();
   assertFalse("Returned book list should not be empty", books.isEmpty());

This test case first loads the data from /books/books.json which is present in /test/resources folder. After setting up of data, the test case runs and asserts that database should return some list of books.

@UsingDataSet(loadStrategy = LoadStrategyEnum.CLEAN_INSERT, locations = "/books/empty.json")
@ShouldMatchDataSet(location = "/books/book1.json")
public void addBook(){
   Book book = Book.builder()
         .author("Joshua Bloch")
         .categories("Programming", "Java")
         .yearOfPublishing(2008, Month.MAY)
         .title("Effective Java")

This will first load an empty json in database to ensure everything is clean. Then test case will run which will insert a book. Then @ShouldMatchDataSet will match the database data with the /books/book1.json and if the data matches the test case will pass. Below is the book1.json file which is used by this test case.

  "books": [
      "title": "Effective Java",
      "author": "Joshua Bloch",
      "publishedYear": {
        "year": 2008,
        "month": 5
      "categories": [
      "publisher": "Addison-Wesley",
      "isbnCode": 1234567890

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