I am writing unit test. I need to mock ObjectId. How can I do this?

const mockTokenDto: CreateUserTokenDto = {
  token: 
    'a172c98424ad6c6269d398de476940e29feacea5f8ab270ecbc45262ec1d6f04a4abd223925bb0759e915f96c7aaf196',
  userId: '5fa1c587ae2ac23e9c46510f',
  expireAt: '2020-11-04T21:06:26.236Z',
}


export class CreateUserTokenDto {
  @IsString()
  token: string;
  @IsString()
  userId: mongoose.Types.ObjectId;
  @IsDateString()
  expireAt: string;
}

I am writing unit test. I need to mock ObjectId. How can I do this?

const mockTokenDto: CreateUserTokenDto = {
  token: 
    'a172c98424ad6c6269d398de476940e29feacea5f8ab270ecbc45262ec1d6f04a4abd223925bb0759e915f96c7aaf196',
  userId: '5fa1c587ae2ac23e9c46510f',
  expireAt: '2020-11-04T21:06:26.236Z',
}


export class CreateUserTokenDto {
  @IsString()
  token: string;
  @IsString()
  userId: mongoose.Types.ObjectId;
  @IsDateString()
  expireAt: string;
}

• javascript
• mongodb
• unit-testing
• mongoose
• nestjs

• You can just create it with exsiting model const mockUser = new <UserModel>({data}) and save it later with mockUser.save() – anttud Commented Nov 4, 2020 at 6:25
• I dont understand – Pawel Commented Nov 4, 2020 at 7:03
• Here it is explained in the documentation – anttud Commented Nov 4, 2020 at 7:18

3 Answers 3

Found another way to mock ObjectId generation. Just mock ObjectID.generate. For example, mock with constant:

const { BSON } = require('bson');
jest.spyOn(BSON.ObjectID.prototype, 'generate').mockImplementation(() => {
    return Buffer.from('62a23958e5a9e9b88f853a67', 'hex');
});

Mock implementation can be replaced with chained 'mockImplementationOnce', if more than one id need to be generated

Jest mock for ObjectID

The accepted answer is not a mock.. it is a real ObjectId

If you came here looking to solve the problem of ever changing ObjectIds in your snapshots / tests then look no furhter.

Unfortunately mocking mongoose.Types.ObjectId is not easy, if you try to spyOn or jest.fn() the exported type from mongoose you will get errors relating to primitive types.

Here is the solution:

Create a wrapper around mongoose.Types.ObjectId

This makes it easy to re-use the type across your codebase anyway,

import mongoose from 'mongoose';

export type ObjectId = mongoose.Types.ObjectId;
export const ObjectId = mongoose.Types.ObjectId;

Spy on this wrapper in your setup file

https://jestjs.io/docs/configuration#setupfiles-array

import * as ObjectIdWrapper from '../../src/shared/classes/object-id';


const mockId = new ObjectIdWrapper.ObjectId('62a23958e5a9e9b88f853a67');
const ObjectIdSpy = jest.spyOn(ObjectIdWrapper, 'ObjectId');

ObjectIdSpy.mockImplementation(() => mockId);

You can create a mock ObjectId using mongoose.Types.ObjectId

 const mockObjectId = new mongoose.Types.ObjectId();

 const mockTokenDto: CreateUserTokenDto = {
  token: 
    'a172c98424ad6c6269d398de476940e29feacea5f8ab270ecbc45262ec1d6f04a4abd223925bb0759e915f96c7aaf196',
  userId: mockObjectId,
  expireAt: '2020-11-04T21:06:26.236Z',
}

You can learn more about it here https://mongoosejs./docs/api/mongoose.html#types-objectid-js