@jest-mock/express

A lightweight Jest mock for unit testing Express

Getting Started

Installation:

yarn add --dev @jest-mock/express

npm install --save-dev @jest-mock/express

Importing:

import { getMockReq, getMockRes } from '@jest-mock/express'

Usage

Request - getMockReq

getMockReq is intended to mock the req object as quickly as possible. In its simplest form, you can call it with no arguments to return a standard req object with mocked functions and default values for properties.

const req = getMockReq()

To create a mock req with provided values, you can pass them to the function in any order, with all being optional. The advantage of this is that it ensures the other properties are not undefined. Loose type definitions for standard properties are provided, custom properties ([key: string]: any) will be passed through to the returned req object.

// an example GET request to retrieve an entity
const req = getMockReq({ params: { id: '123' } })

// an example PUT request to update a person
const req = getMockReq({
  params: { id: 564 },
  body: { firstname: 'James', lastname: 'Smith', age: 34 },
})

For use with extended Requests, getMockReq supports generics.

interface AuthenticatedRequest extends Request {
  user: User
}

const req = getMockReq<AuthenticatedRequest>({ user: mockUser })

// req.user is typed
expect(req.user).toBe(mockUser)

Response - getMockRes

getMockRes will return a mocked res object with Jest mock functions. Chaining has been implemented for the applicable functions.

const { res, next, clearMockRes } = getMockRes()

All of the returned mock functions can be cleared with a single call to mockClear. An alias is also provided called clearMockRes.

const { res, next, mockClear } = getMockRes()

beforeEach(() => {
  mockClear() // can also use clearMockRes()
})

It will also return a mock next function for convenience. next will also be cleared as part of the call to mockClear/clearMockRes.

To create mock responses with provided values, you can provide them to the function in any order, with all being optional. Loose type definitions for standard properties are provided, custom properties ([key: string]: any) will be passed through to the returned res object.

const { res, next, clearMockRes } = getMockRes({
  locals: {
    user: getLoggedInUser(),
  },
})

For use with extended Responses, getMockRes supports generics.

interface CustomResponse extends Response {
  locals: {
    sessionId?: string
    isPremiumUser?: boolean
  }
}

const { res } = getMockRes<CustomResponse>({
  locals: {
    sessionId: 'abcdef',
    isPremiumUser: false,
  },
})

// res.locals is typed
expect(res.locals.sessionId).toBe('abcdef')
expect(res.locals.isPremiumUser).toBe(false)

Example

A full example to test a controller could be:

// generate a mocked response and next function, with provided values
const { res, next } = getMockRes({
  locals: {
    isPremiumUser: true,
  },
})

test('will respond with the entity from the service', async () => {
  // generate a mock request with params
  const req = getMockReq({ params: { id: 'abc-def' } })

  // provide the mock req, res, and next to assert
  await myController.getEntity(req, res, next)

  expect(res.json).toHaveBeenCalledWith(
    expect.objectContaining({
      id: 'abc-def',
    }),
  )
  expect(next).toBeCalled()
})