Examples of testing with Jest and Promises

promise.test.js

test('promise series', () => {
  new Promise(resolve => {
    resolve('a');
  }).then(Promise.resolve());
});

const fetchBeverageList = () =>
  new Promise((resolve, reject) => {
    resolve(4);
  });

test('resolving promise', () =>
  new Promise((resolve, reject) => {
    resolve(); // change to reject();, and it will fail
  }));

test('4 is 4', () => {
  fetchBeverageList().then(four => expect(four).toBe(4));
});

const fivePromise = () => new Promise(a => a(5));
const failingFivePromise = () => new Promise(reject => reject(5));

test('expect 5', () => fivePromise().then(five => expect(five).toBe(5)));

test('expect 5, fail', () =>
  failingFivePromise().catch(five => expect(five).toBe(5)));