def test_validate_format_none():
    with pytest.raises(ValueError):
        time.validate_format(None)
def test_validate_format():
    assert time.validate_format('%Y') == '%Y'
    assert time.validate_format('%Y%m%d') == '%Y%m%d'
    assert time.validate_format('%b %d %Y %H:%M:%S') == '%b %d %Y %H:%M:%S'
    assert time.validate_format('some text') == 'some text'