In Vitest, how do I assert that a console.log() happened?

Question

The question's in the title. With Jest it was console.log = jest.fn(). How do I get and analyse the console output of the code I'm testing?

Brownstone

Answer 1

import { afterAll, describe, it, expect, vi } from 'vitest';

describe('should mock console.log', () => {
  const consoleMock = vi.spyOn(console, 'log').mockImplementation(() => undefined);

  afterAll(() => {
    consoleMock.mockReset();
  });

  it('should log `sample output`', () => {
    console.log('sample output');
    expect(consoleMock).toHaveBeenCalledOnce();
    expect(consoleMock).toHaveBeenLastCalledWith('sample output');
  });
});

Jumpoff

exemplary answer – Soracco

how to assert that some console.log contained the string 'hey'? – Tennessee

Answer 2

Thanks a lot for your answer @Yokozuna59!

For others, if you still want to see the console log output, just define:

const consoleSpy = vi.spyOn(console, 'log')

without the mockImplementation().

Scarberry