My jest test is failing for my controller with a json method missing error

I have a controller that registers a user, however, testing it does not work. I am using Jest in Node version 16. Here is the controller: I get the following error
TypeError: response.status(...).json is not a function

I did implement the json method of the object so I don't know why I'm getting this error

        class AuthenticationController {

        registerNewUser = async(request:Request, response:Response, next:NextFunction) =>{
            const username = request.body.username
            const password = request.body.password
            if(!username || !password){
                
                response.status(400).json({success:false, 'no username or password'}) 
            }
            const query = {username: username}
            const user = await User.findOne(query)
            if(user){
               response.status(400).json({message: 'User exists'})
            } 
            const hashUtility = new HashUtil()
            const {hash}  = hashUtility.createHash(password)
            const createQuery = (username: username,hash:hash)
            await User.create( createQuery)
            // TypeError: response.status(...).json is not a function
            // is now thrown here
            response.status(200).json(createQuery)   
        }
    
    
    }

    export {AuthenticationController}

Here is my test class

    describe('UserAuthController test suite', ()=>{
            let authController:AuthenticationController 
           
            beforeEach(()=>{
               authController  = new AuthenticationController()
            })
           it('should successfully register a new user ', async ()=>{
             let user  = new User({
                username: 'user@gmail.com',
                hash: 'ddh44500000',
              })
           
            let mockRequest = {
                body: {
                username: 'user@gmail.com',
                password: 'mypassword'
               }
             }
            let responseObject = {};
            let mockResponse: Partial<Response> = {
              statusCode: 200,
              status: jest.fn().mockImplementation(()=>200),
              json: jest.fn().mockImplementation((result) =>{
                responseObject = result
              })
          }
             UserConfig.findOne = 
                 jest.fn().mockImplementation((query)=>{
                   return null
             })
             let next = jest.fn()
             let hashUtility = new HashUtil()
             jest.spyOn(hashUtility, 'createHash').mockImplementationOnce((password) =>{
               return {hash: 'ddh44500000'}
              })
            await authController.registerNewUser(mockRequest as Request, mockResponse as 
            Response, next)
            console.log(`ResponseObjeect ${responseObject}`)
       })
     })

I don't know what I'm missing in my test code. Please help

The problem is that you're not creating your mockResponse object properly.

You're response object's methods should support method chaining as described in your code:

 response.status(200).json({ message: "msg" });

In order to be able to call .json({ message: "msg" }) the previous status method must return this (the response object).

But in you're test code you've the following:

let mockResponse: Partial<Response> = {
  statusCode: 200,
  status: jest.fn().mockImplementation(() => 200),
  json: jest.fn().mockImplementation((result) => {
    responseObject = result;
  }),
};

So, when you pass this mock response object to the middle-ware and it calls response.status(400) it returns 200 (according to your jest.fn().mockImplementation(() => 200)).

Then it chains the .json({}) call but as the returned value from previous call was 200, so (200).json({...}) throws an error:

> TypeError: response.status(...).json is not a function

This is an easy fix, you just need to return the mockResponse object from each mock methods, like the following snippet:

let responseObject = {};
let mockResponse = {
  statusCode: 200,
  status: jest.fn().mockImplementation((status) => mockResponse),
  json: jest.fn().mockImplementation((result) => {
    responseObject = result;
    return mockResponse
  }),
};