Mocking Express Request with Jest and Typescript using correct types

Question

I have been having some trouble getting the correct Express Request type working in Jest. I have a simple user registration passing with this code:

import { userRegister } from '../../controllers/user'; import { Request, Response, NextFunction } from 'express';  describe('User Registration', () => {   test('User has an invalid first name', async () => {     const mockRequest: any = {       body: {         firstName: 'J',         lastName: 'Doe',         email: '[email protected]',         password: 'Abcd1234',         passwordConfirm: 'Abcd1234',         company: 'ABC Inc.',       },     };      const mockResponse: any = {       json: jest.fn(),       status: jest.fn(),     };      const mockNext: NextFunction = jest.fn();      await userRegister(mockRequest, mockResponse, mockNext);      expect(mockNext).toHaveBeenCalledTimes(1);     expect(mockNext).toHaveBeenCalledWith(       new Error('First name must be between 2 and 50 characters')     );   }); }); 

However, if I change:

    const mockRequest: any = {       body: {         firstName: 'J',         lastName: 'Doe',         email: '[email protected]',         password: 'Abcd1234',         passwordConfirm: 'Abcd1234',         company: 'ABC Inc.',       },     }; 

to:

const mockRequest: Partial<Request> = {   body: {     firstName: 'J',     lastName: 'Doe',     email: '[email protected]',     password: 'Abcd1234',     passwordConfirm: 'Abcd1234',     company: 'ABC Inc.',   }, }; 

From the TypeScript documentation (https://www.typescriptlang.org/docs/handbook/utility-types.html#partialt), this should make all fields on the Request object optional.

However, I get this error:

Argument of type 'Partial<Request>' is not assignable to parameter of type 'Request'.   Property '[Symbol.asyncIterator]' is missing in type 'Partial<Request>' but required in type 'Request'.ts(2345) stream.d.ts(101, 13): '[Symbol.asyncIterator]' is declared here. 

I was hoping that someone with a little more TypeScript experience could comment and let me know what I am doing wrong.

Answer 1

Your mock data type doesn't have to perfectly fit the actual data. Well, it doesn't by definition. It's just a mock, right?

What you need is a type assertion. It's a way to tell TypeScript "Okay bro, I know what I'm doing here.".

This is not a production code, it's a test. You're probably even running it in watch mode. We can reject some type safety here without problem. TypeScript doesn't know it's a mock, but we do.

const mockRequest = {     body: {     firstName: 'J',     lastName: 'Doe',     email: '[email protected]',     password: 'Abcd1234',     passwordConfirm: 'Abcd1234',     company: 'ABC Inc.',     }, } as Request; 

If something crashes during the test, because mockRequest isn't similar to Request enough, we'll know and we'll fix the mock, add some new properties etc.

If as Request doesn't work you can tell TypeScript "I REALLY know what I'm doing here" by asserting to any or unknown first and then to the type you need. It would look like

const x: number = "not a number :wink:" as any as number; 

It's useful when we'd like to test that our code doesn't work well with bad input.

For your particular case -- mocking express Request -- there is jest-express to help you, if you can spare the node_modules size of course.