I think require('fs') in an ESM output file will throw ReferenceError: require is not defined at runtime on Node.js 20-21 (only 22.12+ made require available in ESM). Since the tool supports Node >= 20, should this be import { existsSync } from 'fs' at the top of the file instead? I could be wrong on this.

--fix runs sudo apt/dnf install with -y and no user confirmation beyond the flag itself. Should this prompt before escalating to root?

Every test just asserts resolves.not.toThrow() - none verify the actual behavior (logged messages, execa call args, return values). These will pass even if the implementation is completely wrong. The test names say "should detect when X" but nothing is actually detected or asserted.

Something like:

it('should detect when Node.js version is too old', async () => {
  const logSpy = jest.spyOn(console, 'log').mockImplementation(() => {});

  Object.defineProperty(process, 'version', {
    value: 'v18.0.0',
    writable: true,
  });

  const { runDoctor } = await import('../doctor.js');
  await runDoctor(false);

  expect(logSpy).toHaveBeenCalledWith(
    expect.stringContaining('Node.js version v18.0.0 is not supported')
  );
});

nit: unnecessary comment. There are a few of these - where the comment doesn't add value - just repeats what the line below easily reads on its own.