Cannot mock a function in Jest-CodePudding

I'm trying to mock a service function that is being called by a controller class. I already mocked the service by using jest.mock() but I can't seem to mock the response of the service function. Can anybody spot what's wrong and how I should do it correctly?

MyController.ts

import {MyService} from '@service/MyService';

export class MyController {

  constructor() {  }

  public async queryDataById(id: string) {
    const myService = new MyService();
    return myService.query(id);
  }

}

MyController.test.ts

import { MyController } from "@controller/MyController";
import { MyService } from "@service/MyService";

jest.mock("@service/MyService")

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

    describe("queryDataByid", () => {

        it("should return a response", async () => {
            const response = {
                id: 1,
                data: {}
            }
            MyService.query.mockReturnValue(response)
            const result = await controller.queryDataById(1)
            expect(result).toBeDefined()
            expect(result).toBe(response)
        })
    })
})

Error

Property 'query' does not exist on type 'typeof MyService'.ts(2339)

CodePudding user response：

Seems we wrongly specified the method name of MyService in test file.

MyService.queryDataById.mockReturnValue(response)

it is supposed to be query not queryDataById

Here is the sample working tests. I don't use jest.mock here, I used prototype mocking.

describe('MyController', () => {
  let controller: MyController = new MyController();

  describe('queryDataByid', () => {
    it('should return a response', async () => {
      const response = {
        id: 1,
        data: {},
      };

      MyService.prototype.query = jest.fn().mockReturnValue(response); // prototype mocking

      const result = await controller.queryDataById('1');

      expect(result).toBeDefined();
      expect(result).toBe(response);
    });
  });
});

Result

  MyController
    queryDataByid
      ✓ should return a response (2 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        1.433 s, estimated 2 s
Ran all test suites.

CodePudding user response：

Also, found another way to resolve this and it's by using jest.spyOn()

Sample:

spyQuery = jest.spyOn(MyService.prototype, "query")
spyQuery.mockResolvedValue(queryResult)