An example of testing setTimeOut and useState hook rerender

FlashMessage.test.js

import React from "react";
import { mount } from "enzyme";
import FlashMessage from "./FlashMessage";
import { act } from "react-dom/test-utils";

describe("FlashMessage", () => {
  let container, messageMock;
  beforeEach(() => {
    jest.useFakeTimers();
    messageMock = "Test message";
    container = mount(<FlashMessage message={messageMock} />);
  });
  it("Renders component", () => {
    expect(container.length).toEqual(1);
  });

  it("Displays message", () => {
    expect(container.text()).toEqual(messageMock);
  });

  it("Displays message", () => {
    act(() => {
      jest.runAllTimers();
      container.update()
    });
    expect(container.text()).toEqual("");
  });
});