Use export default instance instead of export {instance}

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.
• Using jest functions like mockImplementation in TypeScript: Typescript and Jest: Avoiding type errors on mocked functions