How to test useRef with Jest and react-testing-library? - reactjs

Question

I'm using create-react-app, Jest and react-testing-library for the configuration of the chatbot project.
I have a functional component that uses useRef hook. When a new message comes useEffect hook is triggered and cause scrolling event by looking a ref's current property.
const ChatBot = () => {
const chatBotMessagesRef = useRef(null)
const chatBotContext = useContext(ChatBotContext)
const { chat, typing } = chatBotContext
useEffect(() => {
if (typeof chatMessagesRef.current.scrollTo !== 'undefined' && chat && chat.length > 0) {
chatBotMessagesRef.current.scrollTo({
top: chatMessagesRef.current.scrollHeight,
behavior: 'smooth'
})
}
// eslint-disable-next-line
}, [chat, typing])
return (
<>
<ChatBotHeader />
<div className='chatbot' ref={chatBotMessagesRef}>
{chat && chat.map((message, index) => {
return <ChatBotBoard answers={message.answers} key={index} currentIndex={index + 1} />
})}
{typing &&
<ServerMessage message='' typing isLiveChat={false} />
}
</div>
</>
)
}
I want to be able to test whether is scrollTo function triggered when a new chat item or typing comes, do you have any ideas? I couldn't find a way to test useRef.

Answer 1

You can move your useEffect out of your component and pass a ref as a parameter to it. Something like
const useScrollTo = (chatMessagesRef, chat) => {
useEffect(() => {
if (typeof chatMessagesRef.current.scrollTo !== 'undefined' && chat && chat.length > 0) {
chatBotMessagesRef.current.scrollTo({
top: chatMessagesRef.current.scrollHeight,
behavior: 'smooth'
})
}
}, [chat])
}
Now in your component
import useScrollTo from '../..'; // whatever is your path
const MyComponent = () => {
const chatBotMessagesRef = useRef(null);
const { chat } = useContext(ChatBotContext);
useScrollTo(chatBotMessagesRef, chat);
// your render..
}
Your useScrollTo test:
import useScrollTo from '../..'; // whatever is your path
import { renderHook } from '#testing-library/react-hooks'
it('should scroll', () => {
const ref = {
current: {
scrollTo: jest.fn()
}
}
const chat = ['message1', 'message2']
renderHook(() => useScrollTo(ref, chat))
expect(ref.current.scrollTo).toHaveBeenCalledTimes(1)
})