react-testing-library.js

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

test("username doesn't exist", () => {
  const { queryByTestId } = render(
    <Avatar
      username="Timonweb"
      src="https://example.com/avatar.jpg"
      usernameIsHidden
    />
  );
  expect(queryByTestId(/username/i)).toBeNull();
});