Mocking Mongoose model with jest

Question

I am trying to mock a mongoose model with jest, but is getting Cannot create property 'constructor' on number '1' error. I was able to reproduce the issue by creating the project with 2 files shown below. Is there a way to mock a mongoose model with jest?

./model.js

const mongoose = require('mongoose')
const Schema = mongoose.Schema

const schema = new Schema({
  name: String
})

module.exports = mongoose.model('Test', schema)

./model.test.js

jest.mock('./model')
const Test = require('./model')

// Test.findOne.mockImplementation = () => {
//   ...
// }

Error:

 FAIL  ./model.test.js
  ● Test suite failed to run

    TypeError: Cannot create property 'constructor' on number '1'

      at ModuleMockerClass._generateMock (../../jitta/sandbox/rest_api/node_modules/jest-mock/build/index.js:458:34)
      at Array.forEach (native)
      at Array.forEach (native)
      at Array.forEach (native)

Update:

Seems to be a bug in jest. https://github.com/facebook/jest/issues/3073

Answer 1

An other solution is to spyOn the model prototype functions.

For example, this will make MyModel.save() fail :

    jest.spyOn(MyModel.prototype, 'save')
      .mockImplementationOnce(() => Promise.reject('fail update'))

You can use mockImplementationOnce to not having to mockRestore the spy. But you can also use mockImplementation and use something like :

afterEach(() => {
  jest.restoreAllMocks()
})

Tested with "mongoose": "^4.11.7" and "jest": "^23.6.0".

Answer 2

ok, i had the same problem so i author this package to solve this problem: https://www.npmjs.com/package/mockingoose

this is how you can use it let's say this is your model:

import mongoose from 'mongoose';
const { Schema } = mongoose;

const schema = Schema({
    name: String,
    email: String,
    created: { type: Date, default: Date.now }
})

export default mongoose.model('User', schema);

and this is your test:

it('should find', () => {
  mockingoose.User.toReturn({ name: 2 });

  return User
  .find()
  .where('name')
  .in([1])
  .then(result => {
    expect(result).toEqual({ name: 2 });
  })
});

checkout the tests folder for more examples: https://github.com/alonronin/mockingoose/blob/master/___tests___/index.test.js

no connections is made to the database!