unit testing reactJS

I'm not sure how to go about this. I've watched a few tutorials but I can't grasp the concept. I want to implement Unit testing on this function - Help! please.

The function returns a joke from the API using the button and renders the joke in a h5 tag.

function Random() {
    const [joke, setJoke] = useState()
    const newJoke = () => {
        fetch("http://api.icndb.com/jokes/random")

            .then(result => result.json())
            .then(result2 => {
                console.log(result2)
                setJoke(result2.value.joke)
            })
            .catch(error => {
                console.log(error);
            });
    }

HTML (render):

<h5 class="card-title">{joke}</h5>
    <button name="Randombtn" class="btn btn-primary" onClick={() => newJoke()}>click here for another chuckle</button>

I've looked into Jest but dont know how to apply it to this.