how to mock a nested response object parameter in jest?-CodePudding

I am writing a unit tests for this specific endpoint but I can't mock the Response Parameter, it is throwing an error in the .json part whenever it tries to access it.

async createTenant(@Body() clientDto: ClientDto, @Res() res: any)

This is where I access it inside the controller. It is throwing an error inside the .json function, how do I mock this property?

return res.status(HttpStatus.BAD_REQUEST).json({
    message: 'Client already exists.',
});

I already tried something like this:

const jsonFn = jest.fn().mockImplementation().mockResolvedValueOnce({ message: 'something' });
const res = { status: jest.fn().mockResolvedValueOnce({ json: jsonFn })};

It is now working for the .status part but for the .json it is still throwing an error. Any ideas that might help?

CodePudding user response：

You should try using a library to mock the Request and Response objects, the best one I have found so far is @jest-mock/express.

You can use it like this:

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


const { res } = getMockRes();

You can similarly mock Request as well, the docs are very clear on the usage.

CodePudding user response：

There are many ways we can reason about this.

For example, imagine the following controller:

import { Body, Controller, Get, HttpStatus, Res } from "@nestjs/common";

export class TestDto {
  hello?: string;
}

@Controller()
export class TestController {
  @Get()
  public async create(
    @Body() testDto: TestDto,
    @Res() res: any
  ): Promise<string> {
    res
      .status(HttpStatus.BAD_REQUEST)
      .json({ message: "i'm testting a bad request" });

    return testDto.hello ?? "hello is missing";
  }
}

We can test the calls made to status and json:

describe("TestController", () => {
  let controller: TestController;

  const mockJson = jest.fn().mockImplementation(() => null),
    mockStatus = jest.fn().mockImplementation(() => ({ json: mockJson })),
    mockResponse = {
      status: mockStatus,
    },
    mockDto = { hello: "world" };

  beforeEach(() => {
    jest.clearAllMocks();
  });

  beforeEach(async () => {
    const module = await Test.createTestingModule({
      providers: [TestController],
    }).compile();

    controller = module.get(TestController);
  });

  beforeEach(async () => {
    await controller.create(mockDto, mockResponse);
  });

  it("checks call to status", () => {
    expect(mockStatus).toHaveBeenCalledWith(HttpStatus.BAD_REQUEST);
  });

  it("checks call to json", () => {
    expect(mockJson).toHaveBeenCalledWith({
      message: "i'm testting a bad request",
    });
  });
});