mock-req-res

Extensible mock req / res objects for use in unit tests of ExpressJS controller and middleware functions.

Prerequisites

This library assumes:

You are using NodeJS 8+
You write properly isolated unit tests of route controllers and ExpressJS middleware functions
You use sinon version 5 or better.

Install

Add mock-req-res as a devDependency:

npm i -D mock-req-res

Mocking `req`.

To test a controller or middleware function you need to mock a request object.

Do this with:

const req = mockRequest(options)

The options can be anything you wish to attach or override in the request.

The vanilla mockRequest gives you the following properties.

body: {},
cookies: {},
query: {},
params: {},
headers: {},
get: stub()

Mocking `res`.

To test a route controller or middleware function you also need to mock a response object.

Do this with:

const res = mockResponse(options)

The options can be anything you wish to attach or override in the request.

The vanilla mockResponse gives you the following functions, in the form of sinon spies and stubs.

clearCookie: spy(),
cookie: spy(),
download: spy(),
end: spy(),
format: spy(),
getHeader: spy(),
json: spy(),
jsonp: spy(),
redirect: spy(),
render: spy(),
send: spy(),
sendFile: spy(),
sendStatus: spy(),
setHeader: spy(),
set: spy(),
type: spy(),
get: stub(),
status: stub().returns(res), // returns itself, allowing chaining
vary: stub().returns(res) // returns itself, allowing chaining

Note you can always add other spies or stubs as needed via the options.

Example

Let's say you have a route controller like this:

const save = require('../../utils/saveThing') // assume this exists.

const createThing = async (req, res) => {
  const { name, description } = req.body
  if (!name || !description) throw new Error('Invalid Properties')
  const saved = await save({ name, description })
  res.json(saved)
}

To unit test this you could use Mocha, Chai, Sinon, and Proxyquire as follows:

const { expect } = require('chai')
const { stub, match } = require('sinon')
const { mockRequest, mockResponse } = require('mock-req-res')
const proxyquire = require('proxyquire')

describe('src/api/things/createThing', () => {
  const mockSave = stub()

  const createThing = proxyquire('../../src/api/things/createThing', {
    '../../utils/saveThing': mockSave
  })

  const res = mockResponse()

  const resetStubs = () => {
    mockSave.resetHistory()
    res.json.resetHistory()
  }

  context('happy path', () => {
    const name = 'some name'
    const description = 'some description'

    const req = mockRequest({ body: { name, description } })
    const expected = { name, description, id: 1 }
    before(async () => {
      save.returns(expected)
      await createThing(req, res)
    })

    after(resetStubs)

    it('called save with the right data', () => {
      expect(save).to.have.been.calledWith(match({ name, description }))
    })

    it('called res.json with the right data', () => {
      expect(res.json).to.have.been.calledWith(match(expected))
    })
  })

  // and also test the various unhappy path scenarios.
})