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Version: 25.x

Un exemplu asincron

În primul rând, activează suportul Babel în Jest după documentația din ghidul Noţiuni de bază.

Let's implement a module that fetches user data from an API and returns the user name.

// user.js
import request from './request';
export function getUserName(userID) {
return request('/users/' + userID).then(user => user.name);
}

In the above implementation, we expect the request.js module to return a promise. We chain a call to then to receive the user name.

Now imagine an implementation of request.js that goes to the network and fetches some user data:

// request.js
const http = require('http');
export default function request(url) {
return new Promise(resolve => {
// This is an example of an http request, for example to fetch
// user data from an API.
// This module is being mocked in __mocks__/request.js
http.get({path: url}, response => {
let data = '';
response.on('data', _data => (data += _data));
response.on('end', () => resolve(data));
});
});
}

Because we don't want to go to the network in our test, we are going to create a manual mock for our request.js module in the __mocks__ folder (the folder is case-sensitive, __MOCKS__ will not work). Acesta ar putea arăta în felul următor:

// __mocks__/request.js
const users = {
4: {name: 'Mark'},
5: {name: 'Paul'},
};
export default function request(url) {
return new Promise((resolve, reject) => {
const userID = parseInt(url.substr('/users/'.length), 10);
process.nextTick(() =>
users[userID]
? resolve(users[userID])
: reject({
error: 'User with ' + userID + ' not found.',
}),
);
});
}

Acum haideți sa scriem un test pentru funcţionalitatea noastră asincronă.

// __tests__/user-test.js
jest.mock('../request');
import * as user from '../user';
// The assertion for a promise must be returned.
it('works with promises', () => {
expect.assertions(1);
return user.getUserName(4).then(data => expect(data).toEqual('Mark'));
});

Apelăm jest.mock('.. /request') să-i spunem lui Jest să folosească mock-ul nostru creat manual. Se aşteaptă ca valoarea returnată să fie o promisiune care urmează să fie rezolvată. You can chain as many Promises as you like and call expect at any time, as long as you return a Promise at the end.

.resolves#

There is a less verbose way using resolves to unwrap the value of a fulfilled promise together with any other matcher. If the promise is rejected, the assertion will fail.

it('works with resolves', () => {
expect.assertions(1);
return expect(user.getUserName(5)).resolves.toEqual('Paul');
});

async/await#

Writing tests using the async/await syntax is also possible. Here is how you'd write the same examples from before:

// async/await can be used.
it('works with async/await', async () => {
expect.assertions(1);
const data = await user.getUserName(4);
expect(data).toEqual('Mark');
});
// async/await can also be used with `.resolves`.
it('works with async/await and resolves', async () => {
expect.assertions(1);
await expect(user.getUserName(5)).resolves.toEqual('Paul');
});

To enable async/await in your project, install @babel/preset-env and enable the feature in your babel.config.js file.

Tratarea erorilor#

Erorile pot fi tratate prin metoda .catch. Asiguraţi-vă că utilizați expect.assertions pentru a verifica că un anumit număr de aserțiuni sunt executate. Altfel o promisiune rezolvată nu ar eşua testul:

// Testing for async errors using Promise.catch.
it('tests error with promises', () => {
expect.assertions(1);
return user.getUserName(2).catch(e =>
expect(e).toEqual({
error: 'User with 2 not found.',
}),
);
});
// Or using async/await.
it('tests error with async/await', async () => {
expect.assertions(1);
try {
await user.getUserName(1);
} catch (e) {
expect(e).toEqual({
error: 'User with 1 not found.',
});
}
});

.rejects#

The.rejects helper works like the .resolves helper. În cazul în care promisiunea este îndeplinită, testul va eşua automat. expect.assertions(number) is not required but recommended to verify that a certain number of assertions are called during a test. It is otherwise easy to forget to return/await the .resolves assertions.

// Testing for async errors using `.rejects`.
it('tests error with rejects', () => {
expect.assertions(1);
return expect(user.getUserName(3)).rejects.toEqual({
error: 'User with 3 not found.',
});
});
// Or using async/await with `.rejects`.
it('tests error with async/await and rejects', async () => {
expect.assertions(1);
await expect(user.getUserName(3)).rejects.toEqual({
error: 'User with 3 not found.',
});
});

The code for this example is available at examples/async.

If you'd like to test timers, like setTimeout, take a look at the Timer mocks documentation.