How to test if element exists/doesn't exist with Jest and react-testing-library

At first, let's create a simple avatar component:

function Avatar({ username, src, usernameIsHidden = false }) {
  return (
    <div>
      <img src={src} />
      {!usernameIsHidden && <h4 data-testid="username">{username}</h4>}
    </div>
  );
}

The usernameIsHidden flag allows us to toggle visibility of a username.

We'll test username element for existence and non-existence.

1. Here's how to test if the element exists and its content matches our expectation:

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

test("username exists", () => {
  const { getByTestId } = render(
    <Avatar username="Timonweb" src="https://example.com/avatar.jpg" />
  );
  expect(getByTestId(/username/i).textContent).toBe("Timonweb");
});

2. We can also test if the element exists at all:

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

test("username exists", () => {
  const { queryByTestId } = render(
    <Avatar username="Timonweb" src="https://example.com/avatar.jpg" />
  );
  expect(queryByTestId(/username/i)).toBeTruthy();
});

3. Finally, this is how to test for the non-existence of the element:

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();
});

In cases 2 and 3, we use queryByTestId instead of getByTestId. queryByTestId doesn't fail when the queried element doesn't exist, instead, it returns either a value or null and that's what we test with expect().toBeTruthy() and expect().toBeNull().