How do I mock APIs in Jest for my tests?

How do I mock APIs in Jest for my tests?

You can use libraries like jest-fetch-mock or msw to mock API calls in Jest. Would you like a code example?

Yes, please provide a code example using jest-fetch-mock.

Sure! First, install the library: npm install jest-fetch-mock. Then, you can mock a fetch call like this:

import fetchMock from 'jest-fetch-mock';

fetchMock.enableMocks();

beforeEach(() => {
  fetch.resetMocks();
});

test('fetches successfully data from an API', async () => {
  fetch.mockResponseOnce(JSON.stringify({ data: '12345' }));

  const response = await fetch('/api/data');
  const data = await response.json();

  expect(data.data).toEqual('12345');
  expect(fetch).toHaveBeenCalledTimes(1);
});

What if I want to mock a failed API call?

You can mock a failed API call by using mockRejectOnce. Here's an example:

fetch.mockRejectOnce(new Error('API is down'));

const response = await fetch('/api/data');
expect(response).toBeUndefined();