Unit Testing Controllers use Jest, NodeJS

Question

I want to check a case that certain routes are calling the correct controller use Jest specific (mock or spy).

It is case specific for unit testing. Somebody can help me how to check it use jest. I don't need verify kind of expect (status code or res object) i need to check if controller have been called. Thanks!

For instance:

// todoController.js
function todoController (req, res) {
    res.send('Hello i am todo controller')
} 

// index.spec.js
const express = require('express');
const request = require('request-promise');
const todoController = require('./todoController');
jest.mock('./todoController');

const app = express();

app.get('/todo', todoController)

test('If certain routes are calling the correct controller , controller should to have been called times one.', async() => {
    await request({url: 'http://127.0.0.1/todo'})
    expect(todoController).toHaveBeenCalledTimes(1);
})

Solution

Actually if you search, there are many references out there.

In the following, I share a few ways that I know.

One of the big conceptual leaps to testing Express applications with mocked request/response is understanding how to mock a chained

API eg. res.status(200).json({ foo: 'bar' }).

First you can make some kind of interceptor, this is achieved by returning the res instance from each of its methods:

// util/interceptor.js
module.exports = {
  mockRequest: () => {
    const req = {}
    req.body = jest.fn().mockReturnValue(req)
    req.params = jest.fn().mockReturnValue(req)
    return req
  },

  mockResponse: () => {
    const res = {}
    res.send = jest.fn().mockReturnValue(res)
    res.status = jest.fn().mockReturnValue(res)
    res.json = jest.fn().mockReturnValue(res)
    return res
  },
  // mockNext: () => jest.fn()
}

The Express user-land API is based around middleware. AN middleware that takes a request (usually called req), a response (usually called res ) and a next (call next middleware) as parameters.

And then you have controller like this :

// todoController.js
function todoController (req, res) {
    if (!req.params.id) {
      return res.status(404).json({ message: 'Not Found' });
    }

    res.send('Hello i am todo controller')
}

They are consumed by being “mounted” on an Express application (app) instance (in app.js):

// app.js
const express = require('express');
const app = express();

const todoController = require('./todoController');

app.get('/todo', todoController);

Using the mockRequest and mockResponse we’ve defined before, then we’ll asume that res.send() is called with the right payload ({ data }).

So on your test file :

// todo.spec.js
const { mockRequest, mockResponse } = require('util/interceptor')
const controller = require('todoController.js')

describe("Check method \'todoController\' ", () => {
  test('should 200 and return correct value', async () => {
    let req = mockRequest();
    req.params.id = 1;
    const res = mockResponse();

    await controller.todoController(req, res);

    expect(res.send).toHaveBeenCalledTimes(1)
    expect(res.send.mock.calls.length).toBe(1);
    expect(res.send).toHaveBeenCalledWith('Hello i am todo controller');
  });

  test('should 404 and return correct value', async () => {
    let req = mockRequest();
    req.params.id = null;
    const res = mockResponse();

    await controller.todoController(req, res);

    expect(res.status).toHaveBeenCalledWith(404);
    expect(res.json).toHaveBeenCalledWith({ message: 'Not Found' });
  });
});

This is only 1 approach to testing Express handlers and middleware. The alternative is to fire up the Express server.

Comments

[Yusufali2205]

Good example. You can use npmjs.com/package/@jest-mock/express, that way you won't have to implement mockRequest and mockResponse yourself :D.