Jest Testing Framework – Asynchronous Tests

Jest is an open-source testing framework that has become increasingly popular recently. Developed by Facebook and built into the popular packagecreate-react-app. Jest comes with built-in mocking and assertion abilities. In addition, Jest runs your tests concurrently in parallel, providing a smoother, faster test run.

Asynchronous Tests in Jest

Asynchronous Test Using Promises

Sourcecode in jestasync.js file

const axios = require('axios');

const jestasync = {
  fetchUser: () =>
    axios
    .get("https://jsonplaceholder.typicode.com/users/2")
    .then(res => res.data)
    .catch(err => 'error')

};

module.exports=jestasync;

Code in jestasync.test.js file

const jestasync=require('./jestasync');

describe("Asynchronous with Promises", () => {
  test('asynchronous by returning a promise', ()=> {
    expect.assertions(1);

    return jestasync.fetchUser().then(data => {
      expect(data.name).toEqual('Ervin Howell');
    });

  });

  test('asynchronous functions return promises', async ()=> {
    expect.assertions(1);
    const data = await jestasync.fetchUser();
    expect(data.name).toEqual('Ervin Howell');

  });

})

 PASS  ./jestasync.test.js
   Asynchronous
     ✓ asynchronous by returning a promise (135ms)
     ✓ asynchronous functions return promises (40ms)
 

 Test Suites: 1 passed, 1 total
 Tests:       2 passed, 2 total
 Snapshots:   0 total
 Time:        2.121s
 Ran all test suites. 

Asynchronous Using a Callback

Code in jestasync.test.js file

describe("Asynchronous with Callback", () => {

  test("asynchronous callback return data", done => {
    function callback(data) {
      expect(dat.namea).toBe('Ervin Howell');
      done();
    }
    jestasync.fetchUser(callback);
  }, 10000);

});