Typescript Jest says mock or mockReturnedValue do not exist on types I wish to mock

Question

Here's a class I wish to test:

//Request.js
import axios, {AxiosInstance} from 'axios';
import config from './config';

const axiosSingleton: AxiosInstance = axios.create({
  baseURL: 'http://localhost:8080',
});

export default class Request {
  public async get<$ResponseType = any>(url: string): Promise<void> {
    const response = await axiosSingleton.get(url);
    return response.data;
  }
}

when I try testing this by creating a test file, I am not sure how to mock axios. I tried a bunch of ways including - spyOn and automatic mocking. But they don't seem to work. Here's a version of the test file I am not understanding why it doesn't work

// Request.test.js
import axios from 'axios';
import Request from './Request';

interface ITestResponseDataType {
  value: string
}

jest.mock('axios');

describe('Request Tests', () => {
  it('should call axios get with the right relativeUrl', async () => {
    const getMock = jest.fn();

    axios.create.mockReturnValue({
      get: getMock
    });

    getMock.mockResolvedValue({
      value: 'value'
    });

    const data = await new Request().get<ITestResponseDataType>('/testUrl');
    expect(getMock.mock.calls.length).toEqual(1);
    expect(data).toEqual({
      value: 'value'
    });
  });
});

The error I get when I try running the test is -

 TypeScript diagnostics (customize using `[jest-config].globals.ts-jest.diagnostics` option):
    src/common/api/Request.test.ts:15:18 - error TS2339: Property 'mockReturnValue' does not exist on type '(config?: AxiosRequestConfig | undefined) => AxiosInstance'.

    15     axios.create.mockReturnValue({

This error makes sense, because the type defined in axios for axios.create should not allow .mockReturnValue to be called on .create. So how do I tell typescript that jest has gone in and modified it?

Answer 1

Cast the mock method to jest.Mock, ie

import axios from "axios" import Request from "./Request";  // Create an Axios mock // Don't worry about the order, Jest will hoist this above the imports // See https://jestjs.io/docs/manual-mocks#using-with-es-module-imports jest.mock("axios", () => ({   create: jest.fn() }))  // Customise the `create` mock method (axios.create as jest.Mock).mockReturnValue({   get: getMock }) 

Answer 2

Just an addition to top rated answer. I would prefer maintaining type definitions when type casting. That can be be rewritten as

(axios as jest.Mocked<typeof axios>).create.mockReturnValue({   get: getMock }); 

Answer 3

You need to replace the axios.create method with a Jest mock function:

axios.create = jest.fn();

That should allow you to then set its return value.