@applicaster/zapp-react-native-utils/reactHooks/utils/__tests__/index.test.js

Applicaster Zapp React Native utilities package

import { usePrevious, useIsInitialRender } from "../";
import { renderHook, cleanup } from "@testing-library/react-hooks";

describe("usePrevious", () => {
  it("renders", () => {
    const { result } = renderHook(() => usePrevious("test"));
    expect(result).toBeDefined();
    cleanup();
  });

  it("Returns undefined on first call", () => {
    const firstCall = "foo";
    const { result } = renderHook(() => usePrevious(firstCall));
    expect(result.current).not.toBeDefined();
    cleanup();
  });

  it("Returns previously passed value", () => {
    const firstFilm = "Reservoir Dogs";
    const secondFilm = "True Romance";
    const thirdFilm = "Pulp Fiction";

    const { result, rerender } = renderHook(({ film }) => usePrevious(film), {
      initialProps: { film: firstFilm },
    });

    rerender({ film: secondFilm });
    expect(result.current).toEqual(firstFilm);
    rerender({ film: thirdFilm });
    expect(result.current).toEqual(secondFilm);
    cleanup();
  });
});

describe("useIsInitialRender", () => {
  it("returns true if initial render", () => {
    const { result } = renderHook(() => useIsInitialRender());

    expect(result.current).toBe(true);
  });

  it("returns false if on the second render", () => {
    const { result, rerender } = renderHook(() => useIsInitialRender());

    expect(result.current).toBe(true);

    rerender();

    expect(result.current).toBe(false);
  });
});