Learning Redux

Implementations

Let's rewrite the previous example, with a mock implementation that always returns posts:

const getPosts = jest.fn(() => {  return [ { title: 'test' } ]})console.log(getPosts())// output: [ { title: 'test' } ]console.log(getPosts())// output: [ { title: 'test' } ]

Mock implementations also allow us to implement more complicated behavior, such as simulating a callback function:

const getPosts = jest.fn(cb => cb([ { title: 'test' } ]))

Or even a promise:

const getPosts = jest.fn(() =>  Promise.resolve([ { title: 'test' } ]))

It is also possible to define multiple implementations so that the function returns a separate result for different calls, via .mockImplementationOnce:

const getPosts = jest.fn() .mockImplementationOnce(() ...