How do I mock async calls in Jest?

How do I mock async calls in Jest?

You can use Jest's jest.fn() to create a mock function and mockResolvedValue or mockRejectedValue for async calls.

Can you show me an example of that?

Sure! Here's a simple example:

const fetchData = async () => {
  const response = await fetch('https://api.example.com/data');
  return response.json();
};

jest.mock('node-fetch');
const fetch = require('node-fetch');

fetch.mockResolvedValue({ json: jest.fn().mockResolvedValue({ data: 'some data' }) });

// Now you can test fetchData

What if the async call fails?

You can use mockRejectedValue to simulate an error. For example:

fetch.mockRejectedValue(new Error('Fetch failed'));