How to mock axios.create([config]) function to return its instance methods instead of overriding them with mock?

Question

I'm trying to mock axios.create() because I'm using its instance across the app and obviously need all of its implementation which is destroyed by the mock, thus cannot get the result of the get, post method properly.

This is how the code looks like in the actual file:

 export const axiosInstance = axios.create({
        headers: {
           ...headers
        },
        transformRequest: [
            function (data, headers) {
                return data;
            },
        ],
    });
    const response = await axiosInstance.get(endpoint);

And here is the mock setup for axios inside the test file

   jest.mock('axios', () => {
        return {
            create: jest.fn(),
            get: jest.fn(() => Promise.resolve()),
        };
    }
);

How could I get all of the instance methods in the axiosInstance variable instead of just having a mock function which does nothing?

Documentation for axios.create and instance methods: https://github.com/axios/axios#instance-methods

Answer 1

Ended up sticking with the axios mock and just pointing to that mock by assigning the axiosInstance pointer to created axios mock. Basically as @jonrsharpe suggested

Briefly:

import * as m from 'route';
jest.mock('axios', () => {
        return {
            create: jest.fn(),
            get: jest.fn(() => Promise.resolve()),
        };
    }
);
m.axInstance = axios

Would be very nice though if I could have gone without it.

Answer 2

You can use jest's genMockFromModule. It will generate jest.fn() for each of the modules's methods and you'll be able to use .mockReturnThis() on create to return the same instance.

example:

./src/__mocks__/axios.js

const axios = jest.genMockFromModule('axios');

axios.create.mockReturnThis();

export default axios;

working example

---

Edit:

from Jest 26.0.0+ it's renamed to jest.createMockFromModule

Answer 3

Since I need to manage Axios instances, I need a way of retrieving the mocks that are created so I can manipulate the responses. Here's how I did it.

import type { AxiosInstance, AxiosStatic } from 'axios';

const mockAxios = jest.createMockFromModule<AxiosStatic>('axios') as jest.Mocked<AxiosStatic>;

let mockAxiosInstances: jest.Mocked<AxiosInstance>[] = [];

mockAxios.create = jest.fn((defaults) => {
  const mockAxiosInstance = jest.createMockFromModule<AxiosInstance>(
    'axios'
  ) as jest.Mocked<AxiosInstance>;
  mockAxiosInstance.defaults = { ...mockAxiosInstance.defaults, ...defaults };
  mockAxiosInstances.push(mockAxiosInstance);
  return mockAxiosInstance;
});

export function getMockAxiosInstances() {
  return mockAxiosInstances;
}
export function mostRecentAxiosInstanceSatisfying(fn: (a: AxiosInstance) => boolean) {
  return mockAxiosInstances.filter(fn).at(-1);
}
export function clearMockAxios() {
  mockAxiosInstances = [];
}

export default mockAxios;

I added three additional methods:

• clearMockAxios which clears the instance list
• getMockAxiosInstances which gets the list of axios instances that are generated by axios.create
• mostRecentAxiosInstanceSatisfying is a function that will do a filter to get the most recent axios instance that satisfies the predicate. This is what I generally use in the test case since React may render more than expected (or as expected) and I generally just need the last instance.

I use it as follows:

import { getMockAxiosInstances, mostRecentAxiosInstanceSatisfying, clearMockAxios } from '../../__mocks__/axios';

it("...", () => {

  ...
  
  const mockAppClient = mostRecentAxiosInstanceSatisfying(
    a => a.defaults.auth?.username === "myusername"
  );
  mockAppClient.post.mockImplementation(() => {
    return Promise.resolve({ data: "AAA" })
  })

  ... do something that calls the client ...

});

Answer 4

The following code works!

jest.mock("axios", () => {
    return {
        create: jest.fn(() => axios),
        post: jest.fn(() => Promise.resolve()),
    };
});