How can I test React Router with Jest

Question

I'm new to testing with jest and I want to test the following code.

import React from "react";
import "./ButtonLogin.css";
import { Link } from 'react-router-dom';

function ButtonLogin() {
    return (
        <Link to="/login"> <button className="button-login">Iniciar sesión</button></Link>
    )
}

export default ButtonLogin;

import { MemoryRouter } from 'react-router-dom';
import { render, fireEvent, Link } from '@testing-library/react';
import { ButtonLogin } from './ButtonLogin';

it('routes to a new route', async () => {

  ButtonLogin = jest.fn();

  const { getByText } = render(
    <MemoryRouter ButtonLogin={ButtonLogin}>
      <Link to="/login">Iniciar sesión</Link>
    </MemoryRouter>
  );

  fireEvent.click(getByText('Iniciar sesión'));

  expect(ButtonLogin).toHaveBeenCalledWith('/login');
});

I have performed the following test but it fails and I get the following error in line 9. routes to a new route

"ButtonLogin" is read-only.

Answer 1

You can use the createMemoryHistory function and Router component to test it. Create a memory history with initial entries to simulate the current location, this way we don't rely on the real browser environment. After firing the click event, assert the pathname is changed correctly or not.

ButtonLogin.tsx:

import React from 'react';
import { Link } from 'react-router-dom';

function ButtonLogin() {
  return (
    <Link to="/login">
      <button className="button-login">Iniciar sesión</button>
    </Link>
  );
}

export default ButtonLogin;

ButtonLogin.test.tsx:

import { fireEvent, render } from '@testing-library/react';
import React from 'react';
import { Router } from 'react-router-dom';
import ButtonLogin from './ButtonLogin';
import { createMemoryHistory } from 'history';
describe('ButtonLogin', () => {
  test('should change current location to login when button is clicked', () => {
    const history = createMemoryHistory({ initialEntries: ['/home'] });
    const { getByText } = render(
      <Router history={history}>
        <ButtonLogin />
      </Router>
    );
    expect(history.location.pathname).toBe('/home');
    fireEvent.click(getByText('Iniciar sesión'));
    expect(history.location.pathname).toBe('/login');
  });
});

test result:

 PASS  examples/69878146/ButtonLogin.test.tsx (10.675 s)
  ButtonLogin
    ✓ should pass (41 ms)

-----------------|---------|----------|---------|---------|-------------------
File             | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-----------------|---------|----------|---------|---------|-------------------
All files        |     100 |      100 |     100 |     100 |                   
 ButtonLogin.tsx |     100 |      100 |     100 |     100 |                   
-----------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        11.722 s, estimated 12 s

package version: "react-router-dom": "^5.2.0"