How to mock a third party React component using Jest? - reactjs

Question

TLDR; what's the proper way to mock a React component imported from a third-party library?
I'm testing a component called <App/>. It consumes a 3rd part component called <Localize/> provided by a library called localize-toolkit.
I'm having some trouble mocking <Localize/> using Jest.
Here is how I've tried mocking it.
jest.mock('localize-toolkit', () => ({
// Normally you pass in a key that represents the translated caption.
// For the sake of testing, I just want to return the key.
Localize: () => (key:string) => (<span>{key}</span>)
}));
And I've written a unit test for <App/> that looks like this.
it('Test', () => {
const component = render(<App/>);
expect(component).toMatchSnapshot();
}
)
It will pass, however this is the warning message returned.
Functions are not valid as a React child. This may happen if you return a Component instead of <Component /> from render.
And when I look at the snapshot, I get a series of periods "..." where the localized caption should appear.
Am I not mocking the Localize component properly?

Answer 1

Here's how I ended up doing it.
Note how the third-party component Localize needs to be returned as a function.
jest.mock('localize-toolkit', () => ({
Localize: ({t}) => (<>{t}</>)
}));
and in case there are multiple components, and you only want to mock one of them, you can do this:
jest.mock("localize-toolkit", () => {
const lib = jest.requireActual("localize-toolkit");
return {
...lib,
Localize: ({t}) => (<>{t}</>),
};
});

Answer 2

We can mock the 3rd party library for example in my case i need to mock react-lazyload
Component.tsx
import LazyLoad from 'react-lazyload';
render() {
<LazyLoad><img/></LazyLoad>
}
In jest.config.js
module.exports = {
moduleNameMapper: {
'react-lazyload': '/jest/__mocks__/react-lazyload.js',
}
}
In jest/mocks/react-lazyload.js
import * as React from 'react';
jest.genMockFromModule('react-lazyload');
const LazyLoad = ({children}) => <>{children}</>;
module.exports = { default: LazyLoad };