Mocking Mongoose model with jest - node.js

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!

Answer 3

for typescript I found a hack that works
jest.spyOn(model, 'find').mockReturnValueOnce(dummyData as any);

Answer 4

Mockingoose seems to be a very nice solution. But I was also able to mock my model with Jest.mock() function. At least create method.
// in the module under the test I am creating (saving) DeviceLocation to DB
// someBackendModule.js
...
DeviceLocation.create(location, (err) => {
...
});
...
DeviceLocation model definition:
// DeviceLocation.js
import mongoose from 'mongoose';
const { Schema } = mongoose;
const modelName = 'deviceLocation';
const DeviceLocation = new Schema({
...
});
export default mongoose.model(modelName, DeviceLocation, modelName);
DeviceLocation mock in the __mocks__ folder in the same folder as DeviceLocation model:
// __mock__/DeviceLocation.js
export default {
create: (x) => {
return x;
},
};
in the test file:
// test.js
// calling the mock
...
jest.mock('../../src/models/mongoose/DeviceLocation');
import someBackendModule from 'someBackendModule';
...
// perform the test