Learning Redux

Promises

If you use promises instead of callbacks, like we did in our project, Jest provides an easier way to handle asynchronous tests. You can simply return a promise from the test, and Jest will wait for it to resolve. If the promise is rejected, the test will automatically fail. Let's assume our fetchPosts function returns a promise now. Then, our test would look as follows:

test('fetchPosts returns array of posts', () => {

We will use another matcher here, to ensure that a certain number of assertions are called during a test. This is useful when dealing with asynchronous code:

  expect.assertions(1)

Then, we simply return our promise and check the result:

  return fetchPosts() .then(posts => expect(posts).toContain({ title: 'test' })) ...