ImageGallery.test.jsx

import React from "react";
import { render, screen } from "@testing-library/react";

import ImageGallery from "./ImageGallery";

describe("<ImageGallery />", () => {
  const defaultProps = {
    items: [
      {
        original: "test.png",
        thumbnail: "test_thumb.png",
      },
    ],
  };

  it("renders slides", () => {
    render(<ImageGallery {...defaultProps} />);
    const elements = screen.getAllByLabelText("Go to Slide 1");
    // expect a thumbnail and slide label
    expect(elements.length).toBe(2);
  });
});