import React from "react"; import { render, screen } from "@testing-library/react"; import App from "./App"; let listener: ((rect: any) => void) | undefined = undefined; (global as any).ResizeObserver = class ResizeObserver { constructor(ls: ((rect: any) => void) | undefined) { listener = ls; } observe() {} unobserve() {} disconnect() {} }; test("renders learn react link", () => { render(); const linkElement = screen.getByText(/viewer/i); expect(linkElement).toBeInTheDocument(); });