Without using any other libraries:

import * as axios from "axios";

// Mock out all top level functions, such as get, put, delete and post:
jest.mock("axios");

// ...

test("good response", () => {
  axios.get.mockImplementation(() => Promise.resolve({ data: {...} }));
  // ...
});

test("bad response", () => {
  axios.get.mockImplementation(() => Promise.reject({ ... }));
  // ...
});

It is possible to specify the response code:

axios.get.mockImplementation(() => Promise.resolve({ status: 200, data: {...} }));

It is possible to change the mock based on the parameters:

axios.get.mockImplementation((url) => {
    if (url === 'www.example.com') {
        return Promise.resolve({ data: {...} });
    } else {
        //...
    }
});

Jest v23 introduced some syntactic sugar for mocking Promises:

axios.get.mockImplementation(() => Promise.resolve({ data: {...} }));

It can be simplified to

axios.get.mockResolvedValue({ data: {...} });

There is also an equivalent for rejected promises: mockRejectedValue.

Further Reading:

• Jest mocking documentation
• A GitHub discussion that explains about the scope of the jest.mock("axios") line.
• A related question which addresses applying the techniques above to Axios request interceptors.

I used axios-mock-adapter. In this case the service is described in ./chatbot. In the mock adapter you specify what to return when the API endpoint is consumed.

import axios from 'axios';
import MockAdapter from 'axios-mock-adapter';
import chatbot from './chatbot';

describe('Chatbot', () => {
    it('returns data when sendMessage is called', done => {
        var mock = new MockAdapter(axios);
        const data = { response: true };
        mock.onGet('https://us-central1-hutoma-backend.cloudfunctions.net/chat').reply(200, data);

        chatbot.sendMessage(0, 'any').then(response => {
            expect(response).toEqual(data);
            done();
        });
    });
});

You can see it the whole example here:

Service: https://github.com/lnolazco/hutoma-test/blob/master/src/services/chatbot.js

Test: https://github.com/lnolazco/hutoma-test/blob/master/src/services/chatbot.test.js

I could do that following the steps:

1. Create a folder __mocks__/ (as pointed by @Januartha comment)
2. Implement an axios.js mock file
3. Use my implemented module on test

The mock will happen automatically

Example of the mock module:

module.exports = {
    get: jest.fn((url) => {
        if (url === '/something') {
            return Promise.resolve({
                data: 'data'
            });
        }
    }),
    post: jest.fn((url) => {
        if (url === '/something') {
            return Promise.resolve({
                data: 'data'
            });
        }
        if (url === '/something2') {
            return Promise.resolve({
                data: 'data2'
            });
        }
    }),
    create: jest.fn(function () {
        return this;
    })
};