Examining the creation of mongoose model instances with Jest

Question

Examining the creation of mongoose model instances with Jest

Exploring the functionality of a REST API created with express and mongoose, I am utilizing jest and supertest for handling http calls. Despite being new to testing in javascript, I am eager to learn.

Specifically when testing a creation URL, my goal is to ensure that the instantiation is done solely using the req.body object. After researching about mock objects versus stubs and studying Jest documentation, my latest attempt resembles the following:

test('Should correctly instantiate the model using req.body', done => {

  const postMock = jest.fn();

  const testPost = {
    name: 'Test post',
    content: 'Hello'
  };

  postMock.bind(Post); // <- Post represents my model

  // Mocking the save function to avoid database usage
  Post.prototype.save = jest.fn(cb => cb(null, testPost));

  // Making the Supertest call
  request(app).post('/posts/')
  .send(testPost)
  .then(() => {
    expect(postMock.mock.calls[0][0]).toEqual(testPost);
    done();
  })
  .catch(err => {throw err});

});

Furthermore, I am interested in understanding how to deliberately fail a test upon promise rejection, preventing the error message

Timeout - Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL.

from appearing.

javascript unit-testing express mongoose jestjs

Answer 1

Answer №1

Currently, you seem to be conducting more of an integration test rather than focusing on isolating the route handler function and testing it independently.

To improve this, I recommend separating the handler for /posts/ into its own file:

controllers/post-controller.js

const Post = require('./path/to/models/post')

exports.store = async (req, res) => {
  const post = await new Post(req.body).save()
  res.json({ data: post }
}

Then simply integrate the handler where you have defined your routes:

const express = require('express')
const app = express()
const postController = require('./path/to/controllers/post-controller')

app.post('/posts', postController.store)

With this separation, we can now focus on testing our postController.store specifically with req.body. To mock mongoose and avoid actual database interactions, create a mocked version of Post as follows (building upon your existing code):

path/to/models/__mocks__/post.js

const post = require('../post')

const mockedPost = jest.fn()
mockedPost.bind(Post)

const testPost = {
  name: 'Test post',
  content: 'Hello'
}


Post.prototype.save = jest.fn(cb => {
  if (typeof cb === 'function') {
    if (process.env.FORCE_FAIL === 'true') {
      process.nextTick(cb(new Error(), null))
    } else {
      process.nextTick(cb(null, testPost))
    }
  } else {
    return new Promise((resolve, reject) => {
      if (process.env.FORCE_FAIL === 'true') {
        reject(new Error())
      } else {
        resolve(testPost)
      }
    })
  }
})

module.exports = mockedPost

Note the check for process.env.FORCE_FAIL in case you wish to force a failure.

You are now prepared to test the functionality using req.body:

post-controller.test.js

// Loads anything contained in `models/__mocks__` folder
jest.mock('../location/to/models')

const postController = require('../location/to/controllers/post-controller')

describe('controllers.Post', () => {
  /**
   * Mocked Express Request object.
   */
  let req

  /**
   * Mocked Express Response object.
   */
  let res

  beforeEach(() => {
    req = {
      body: {}
    }
    res = {
      data: null,
      json(payload) {
        this.data = JSON.stringify(payload)
      }
    }
  })

  describe('.store()', () => {
    test('should create a new post', async () => {
      req.body = { ... }
      await postController(req, res)
      expect(res.data).toBeDefined()

      ...
    })

    test('fails creating a post', () => {
      process.env.FORCE_FAIL = true
      req.body = { ... }

      try {
        await postController.store(req, res)
      } catch (error) {
        expect(res.data).not.toBeDefined()

        ...
      }
    })

  })
})

This code is untested, but I hope it provides clarity for your testing efforts.

Answer 2

Currently, you seem to be conducting more of an integration test rather than focusing on isolating the route handler function and testing it independently.

To improve this, I recommend separating the handler for /posts/ into its own file:

controllers/post-controller.js

const Post = require('./path/to/models/post')

exports.store = async (req, res) => {
  const post = await new Post(req.body).save()
  res.json({ data: post }
}

Then simply integrate the handler where you have defined your routes:

const express = require('express')
const app = express()
const postController = require('./path/to/controllers/post-controller')

app.post('/posts', postController.store)

With this separation, we can now focus on testing our postController.store specifically with req.body. To mock mongoose and avoid actual database interactions, create a mocked version of Post as follows (building upon your existing code):

path/to/models/__mocks__/post.js

const post = require('../post')

const mockedPost = jest.fn()
mockedPost.bind(Post)

const testPost = {
  name: 'Test post',
  content: 'Hello'
}


Post.prototype.save = jest.fn(cb => {
  if (typeof cb === 'function') {
    if (process.env.FORCE_FAIL === 'true') {
      process.nextTick(cb(new Error(), null))
    } else {
      process.nextTick(cb(null, testPost))
    }
  } else {
    return new Promise((resolve, reject) => {
      if (process.env.FORCE_FAIL === 'true') {
        reject(new Error())
      } else {
        resolve(testPost)
      }
    })
  }
})

module.exports = mockedPost

Note the check for process.env.FORCE_FAIL in case you wish to force a failure.

You are now prepared to test the functionality using req.body:

post-controller.test.js

// Loads anything contained in `models/__mocks__` folder
jest.mock('../location/to/models')

const postController = require('../location/to/controllers/post-controller')

describe('controllers.Post', () => {
  /**
   * Mocked Express Request object.
   */
  let req

  /**
   * Mocked Express Response object.
   */
  let res

  beforeEach(() => {
    req = {
      body: {}
    }
    res = {
      data: null,
      json(payload) {
        this.data = JSON.stringify(payload)
      }
    }
  })

  describe('.store()', () => {
    test('should create a new post', async () => {
      req.body = { ... }
      await postController(req, res)
      expect(res.data).toBeDefined()

      ...
    })

    test('fails creating a post', () => {
      process.env.FORCE_FAIL = true
      req.body = { ... }

      try {
        await postController.store(req, res)
      } catch (error) {
        expect(res.data).not.toBeDefined()

        ...
      }
    })

  })
})

This code is untested, but I hope it provides clarity for your testing efforts.

Examining the creation of mongoose model instances with Jest

Answer №1

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