I have this hook in React I want to write the unit test but I faced the problem that I don't know how I could cover handleScroll function, how can I go to the useEffect to trigger the scroll event?
I tried fireEvent.scroll but not success.
import { useState, useEffect } from 'react';
const scrollWindow = (
fetchOffset: number,
callback: () => void,
preventFetch?: boolean,
) => {
const [isFetching, setIsFetching] = useState(false);
const handleScroll = () => {
const scrollFromBottom = docElem.scrollHeight - docElem.scrollTop - docElem.clientHeight;
if (scrollFromBottom - fetchOffset > 0) return;
setIsFetching(true);
};
useEffect(() => {
window.addEventListener('scroll', handleScroll);
return () => window.removeEventListener('scroll', handleScroll);
}, [isFetching, preventFetch]);
useEffect(() => {
if (!isFetching) return;
callback();
}, [isFetching]);
return [isFetching, setIsFetching];
};
export default scrollWindow;