Mocking modules

Jest has an amazing mocking feature. You can both create your mocks inside the __mocks__ directory adjacent to mocked file or create them programmatically.

Let's create the services/__mocks__/api.js file for our mock.

Let's export the spy function we would use in our test:

export const getMockDataSpy = jest.fn();

Now, let's create the actual mock:

export const getMockData = () => { 
    return new Promise(resolve => 
      getMockDataSpy(() => resolve(mockMessages))) 
}

Since our getMockData is returning a promise, we will return a new Promise and inside it--we will call getMockDataSpy passing a callback function and resolve.

Now, in our ChatScreen test, we will; need to do two things. First, enable our mock using jest.mock('../../services/api'); this will tell Jest to include our mock file in every place where there is an import...