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Unit testing NestJS with mongo in memory...

webeleon profile image Webeleon ・2 min read

Assuming you already installed and configured mongoose in your NestJS project.

For the sake of having something to test we will create a Squid API. The API will provide a random squid gif when called.
You can see the actual implementation in the demo repo.

Writing tests for code that interact with databases is rather painful.

You either have to create test databases and delete them afterward.
You end up writing and debugging a ton of code to clean before after the testing...

Today is the end of your misery!
I am here to save you the trouble of testing. with nestJS, mongoose and MongoDB.... sorry for the others

First, we will need to add a new development package to the project. (link to the Github repository provided at the end of this article)

npm i --save-dev mongodb-memory-server 

Cool, We can now spawn mongo daemon in memory! How awesome is that?
Since I am a lazy brat, I do not want to rewrite the in-memory mongod bootstrapping code.
Let's write a small test utils file that will provide us an easy to import preconfigured root MongooseModule and an helper to close the connection.

import { MongooseModule, MongooseModuleOptions } from '@nestjs/mongoose';
import { MongoMemoryServer } from 'mongodb-memory-server';

let mongod: MongoMemoryServer;

export const rootMongooseTestModule = (options: MongooseModuleOptions = {}) => MongooseModule.forRootAsync({
  useFactory: async () => {
    mongod = new MongoMemoryServer();
    const mongoUri = await mongod.getUri();
    return {
      uri: mongoUri,

export const closeInMongodConnection = async () => {
  if (mongod) await mongod.stop();

Excellent, in-memory plug an play MongoDB daemon!
Let's import that bad boy to our service and controller test.
Don't forget to close the connection in the afterAll function.

import { Test, TestingModule } from '@nestjs/testing';
import { MongooseModule } from '@nestjs/mongoose';

import { SquidService } from './squid.service';
import { closeInMongodConnection, rootMongooseTestModule } from '../test-utils/mongo/MongooseTestModule';
import { SquidSchema } from './model/squid.schema';

describe('SquidService', () => {
  let service: SquidService;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      imports: [
        MongooseModule.forFeature([{ name: 'Squid', schema: SquidSchema }]),
      providers: [SquidService],

    service = module.get<SquidService>(SquidService);

  it('should be defined', () => {

    Write meaningful test

  afterAll(async () => {
    await closeInMongodConnection();

And voila!
You are all set.
Go back to testing the wonderful code you are writing!

Next Time we will handle the case of end to end test for NestJS.


NestJS techniques mongodb
The issue that saved me

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