How can I mock fetch function in Node.js by Jest? - node.js

Question

How can I mock fetch function in Node.js by Jest?
api.js
'use strict'
var fetch = require('node-fetch');
const makeRequest = async () => {
const res = await fetch("http://httpbin.org/get");
const resJson = await res.json();
return resJson;
};
module.exports = makeRequest;
test.js
describe('fetch-mock test', () => {
it('check fetch mock test', async () => {
var makeRequest = require('../mock/makeRequest');
// I want to mock here
global.fetch = jest.fn().mockImplementationOnce(() => {
return new Promise((resolve, reject) => {
resolve({
ok: true,
status,
json: () => {
return returnBody ? returnBody : {};
},
});
});
});
makeRequest().then(function (data) {
console.log('got data', data);
}).catch((e) => {
console.log(e.message)
});
});
});
I tried to use jest-fetch-mock, nock and jest.mock but failed.
Thanks.

Answer 1

You can mock node-fetch using jest.mock. Then in your test set the actual mock response
import fetch from 'node-fetch'
jest.mock('node-fetch', ()=>jest.fn())
describe('fetch-mock test', () => {
it('check fetch mock test', async () => {
var makeRequest = require('../mock/makeRequest');
const response = Promise.resolve({
ok: true,
status,
json: () => {
return returnBody ? returnBody : {};
},
})
fetch.mockImplementation(()=> response)
await response
makeRequest().then(function (data) {
console.log('got data', data);
}).catch((e) => {
console.log(e.message)
});
});
});

Answer 2

import fetch, { Response } from 'node-fetch';
jest.mock('node-fetch');
describe('fetch-mock test', () => {
const mockFetch = fetch as jest.MockedFunction<typeof fetch>;
it('check fetch mock test', async () => {
const json = jest.fn() as jest.MockedFunction<any>;
json.mockResolvedValue({ status: 200}); //just sample expected json return value
mockFetch.mockResolvedValue({ ok: true, json } as Response); //just sample expected fetch response
await makeRequest();
expect(json.mock.calls.length).toBe(1);
})
})