Jest unit testing with components that use node-fetch

I like very much the Fetch API and I tend to use it as much as possible also with node components.

The same, of course, is applicable to my favorite testing framework: Jest; it works brilliantly with React but I highly recommend to use it in other environments as well.

Super easy setup, assertion library, mocking framework, snapshot testing and code coverage; all in one platform.

But this post is about a specific use case: how to unit test with Jest node components that use node-fetch.

There are many libraries that help you to mock fetch but my favorite in this regard is jest-fetch-mock; it has a very nice API and it works really well together with Jest and because of that I’d like to use it in a non-in-browser context as well.

So here it is my standard setup in 3 simple steps:

1. npm install --save-dev jest-fetch-mock
2. add or modify your setupJest.js file with the following code:

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

3. import node-fetch in your test file and mock it as you please:

const fetch = require('node-fetch');
fetch.mockResponse(JSON.stringify({ message: 'YATTA!' }));

You can also find another example here. I hope this helps.