XMLHttpRequest testing in Jest
The jest api has changed a bit. This is what I use. It doesn't do anything but it's enough to render my components.
const xhrMockClass = () => ({
open : jest.fn(),
send : jest.fn(),
setRequestHeader: jest.fn()
})
window.XMLHttpRequest = jest.fn().mockImplementation(xhrMockClass)
and in the test file:
import '../../__mock__/xhr-mock.js'
Here's a TypeScript example working with Jest 26:
function performRequest(callback: any) {
const xhr = new XMLHttpRequest();
xhr.open('GET', 'https://example.com/');
xhr.onreadystatechange = () => {
if (xhr.readyState !== 4 || xhr.status !== 200) return;
callback(xhr.response);
};
xhr.responseType = 'json';
xhr.setRequestHeader('Accept', 'application/json');
xhr.send(null);
}
describe('request', () => {
const xhrMock: Partial<XMLHttpRequest> = {
open: jest.fn(),
send: jest.fn(),
setRequestHeader: jest.fn(),
readyState: 4,
status: 200,
response: 'Hello World!'
};
jest.spyOn(window, 'XMLHttpRequest').mockImplementation(() => xhrMock as XMLHttpRequest);
const callback = jest.fn();
performRequest(callback);
expect(xhrMock.open).toBeCalledWith('GET', 'https://example.com/');
expect(xhrMock.setRequestHeader).toBeCalledWith('Accept', 'application/json');
(xhrMock.onreadystatechange as EventListener)(new Event(''));
expect(callback.mock.calls).toEqual([['Hello World!']]);
});
As mentioned you don't need additional libraries:
// mocks.js is where you could put your mocks (example below)
const mocks = require('./mocks.js')
test('XHR test', () => {
let xhrMock = {
open: jest.fn(),
setRequestHeader: jest.fn(),
onreadystatechange: jest.fn(),
send: jest.fn(),
readyState: 4,
responseText: JSON.stringify(mocks),
status: 200
}
window.XMLHttpRequest = jest.fn(() => xhrMock)
sendData().then((response) => {
// You could do you checks here. Some examples:
expect(xhrMock.setRequestHeader).toBeCalledWith('Cache-Control', 'no-cache')
expect(xhrMock.open).toBeCalledWith('POST', 'you_api_url.com/end_point/')
expect(xhrMock.withCredentials).toBe(false)
let formData = new FormData()
formData.append('firstParam', 'firstParamValue')
expect(yoloRequestMock.send).toBeCalledWith(formData)
expect(JSON.stringify(response)).toBe(JSON.stringify(mocks))
})
// when onload is called, resolve and reject has been initialed.
xhrMock.onreadystatechange()
// the following function is the one which sends the request (to be tested)
function sendData() {
return new Promise(function(resolve, reject) {
let formData = new FormData()
formData.append('firstParam', 'firstParamValue')
let xhr = new XMLHttpRequest()
xhr.withCredentials = false
xhr.onreadystatechange = function () {
if (this.readyState === 4) {
if(xhr.status === 200) {
resolve(JSON.parse(xhr.responseText))
} else {
reject(xhr.responseText)
}
}
}
xhr.open('POST', T2S_VISUAL_SEARCH_PARAMS.t2sVisualSeacchApiUrl)
xhr.setRequestHeader("Cache-Control", "no-cache");
xhr.send(formData)
})
}
}
The file mocks.js
contains the mocks:
module.exports =
{
response: {
body: { ... }
}
}
You can test XHR in Jest without additional packages. This is helper function which creates mock object for XMLHttpRequest:
let open, send, onload, onerror;
function createXHRmock() {
open = jest.genMockFn();
// be aware we use *function* because we need to get *this*
// from *new XmlHttpRequest()* call
send = jest.genMockFn().mockImpl(function(){
onload = this.onload.bind(this);
onerror = this.onerror.bind(this);
});
const xhrMockClass = function () {
return {
open,
send
};
};
window.XMLHttpRequest = jest.genMockFn().mockImpl(xhrMockClass);
}
And you can use it in test as follows:
it('XHR success', () => {
createXHRmock();
// here you should call GET request
expect(open).toBeCalledWith('GET', 'http://example.com', true);
expect(send).toBeCalled();
// call onload or onerror
onload();
// here you can make your assertions after onload
});