How to mock Axios in Jest

There are many ways to mock Axios. The best is axios-mock-adapter. It allows you to intercept requests and respond with mocked data.

Let’s assume we have function that send request.

import axios from "axios";

export async function getMyHexIp() {
    return axios.get("https://ipinfo.io/ip").then((response) => '0x' + response.data.split('.').map((x: string) => parseInt(x).toString(16)).join(''));
}

We can test it with axios-mock-adapter like this:

import axios from "axios";
import MockAdapter from "axios-mock-adapter";
import {describe, beforeAll, afterEach,it, expect} from "@jest/globals";
import {getMyHexIp} from "./getMyHexIp";

describe("External axios call", () => {
    let mock: MockAdapter;

    beforeAll(() => {
        mock = new MockAdapter(axios);

        mock.onGet(`https://ipinfo.io/ip`).reply(200, '69.69.69.69');
    });

    afterEach(() => {
        mock.reset();
    });

    it("getMyHexIp", async () => {
        // when
        const result = await getMyHexIp()

        // then
        expect(mock.history.get[0].url).toEqual(`https://ipinfo.io/ip`);
        expect(result).toEqual('0x45454545');
    });
});

Additional notes about jest setup:

1. Install devDependencies

pnpm add axios
pnpm add -D @jest/globals jest jest-esbuild ts-node axios-mock-adapter

2. Add jest.config.js

import type {Config} from 'jest';
const config: Config = {
  coverageProvider: "v8",
  transform: {
    '^.+\\.(ts|tsx)$': 'jest-esbuild',
  },
};
export default config;

3. Add tsconfig by

npx tsc --init

Off-topic but about jest

Other recommended mock library ioredis-mock.

Usage:

import RedisMock from "ioredis-mock";

const createRedisMockClient = () => {
    return new RedisMock();
};

How i testing version endpoint in Fastify

import pJson from '../package.json'
import { getFastifyServer } from '../src/fastify'

const correctVersion = { name: pJson.name, version: pJson.version }

describe('i can read version', () => {
    it('from rest api', async () => {
        const server = getFastifyServer()
        const result = await server.inject({
            method: 'GET',
            path: '/',
        })

        expect(result.body).toEqual(JSON.stringify(correctVersion))
        expect(result.statusCode).toEqual(200)
        expect(result.headers['content-type']).toContain('application/json')
    })
})