How to use the watchgod.cli.callback function in watchgod

def test_callback(mocker):
    # boring we have to test this directly, but we do
    mock_logger = mocker.patch('watchgod.cli.logger.info')
    callback({1, 2, 3})
    mock_logger.assert_called_once_with('%d files changed, reloading', 3)

def test_simple(mocker, tmpdir):
    mocker.patch('watchgod.cli.set_start_method')
    mocker.patch('watchgod.cli.sys.stdin.fileno')
    mocker.patch('os.ttyname', return_value='/path/to/tty')
    mock_run_process = mocker.patch('watchgod.cli.run_process')
    cli('tests.test_cli.foobar', str(tmpdir))
    mock_run_process.assert_called_once_with(
        Path(str(tmpdir)),
        run_function,
        args=('tests.test_cli.foobar', '/path/to/tty'),
        callback=callback
    )