Testing Hooks Classic.js

import { renderHook, cleanup, act } from "react-hooks-testing-library";
import useLoadActivity from "../useLoadActivity";
import fetchFunctions from "../fetchActivity";
import mockFetchFunction from "../__mocks__/fetchActivity";

describe("Testing a custom hook (without Jooks)", () => {
  it("should load activities properly", async () => {
    const { result } = renderHook(() => useLoadActivity());
    const { activity, next } = result.current;
    // Ok so that's ok, it's indeed null at first
    expect(activity).toBeNull();
    // Then I'm going to force fetching the (mock) data
    act(() => {
      // This is not asynchronous!!
      // There's no way to "wait" for that async function inside to complete
      next();
    });
    await wait(100);
    // It should have been calling the effect at this point, but nothing...
    expect(activity).not.toBeNull();
    expect(activity.activity).toBe("Foo");
  });

  beforeEach(() => {
    fetchMock.mockImplementation(mockFetchFunction.fetchActivity);
  });
  afterEach(cleanup);
});

const fetchMock = jest.spyOn(fetchFunctions, "fetchActivity");

const wait = async wait =>
  new Promise(resolve => setTimeout(resolve, wait || 1));