import { useState, useEffect } from "react";
const useDebounce = (value, delay) => {
 const [debouncedValue, setDebouncedValue] = useState(value);
 useEffect(() => {
 const handler = setTimeout(() => {
 setDebouncedValue(value);
 }, delay);
 return () => {
 clearTimeout(handler);
 };
 }, [value]);
 return debouncedValue;
};
export default useDebounce;

import { renderHook } from "@testing-library/react-hooks";
import useDebounce from "../useDebounce";
jest.useFakeTimers();
jest.spyOn(global, "clearTimeout");
describe("useDebounce", () => {
 test(`it should clear the timeout when unmounting`, () => {
 const value = "test";
 const delay = 1000;
 const { unmount } = renderHook(() => useDebounce(value, delay));
 expect(clearTimeout).not.toHaveBeenCalled();
 unmount();
 expect(clearTimeout).toHaveBeenCalled(); // fails here
 });
});