[python-package] Tests not running without pandas (tests.python_package_test/test_basic.py)

[strobelTha]

Description

If running pytest without an installation of pandas no test is executed and the run is stopped with the following error message:

python_package_test/test_basic.py:519: in <module>
    ???
E   TypeError: pd_Series() takes no arguments

In that line, we can find a test that seems to be supposedly skipped if pandas is not installed. But as far as I know pytest.mark.parametrize is evaluated anyways, making the whole test suit crash. I'm honestly not sure if this is an error on my side. But it looks like an easy thing to oversee if you have pandas installed by default, so I thought I should mention it here.

@pytest.mark.skipif(not PANDAS_INSTALLED, reason='pandas is not installed')
@pytest.mark.parametrize(
    'y',
    [
        np.random.rand(10),
        np.random.rand(10, 1),
        pd_Series(np.random.rand(10)),
        pd_Series(['a', 'b']),
        [1] * 10,
        [[1], [2]]
    ])
@pytest.mark.parametrize('dtype', [np.float32, np.float64])
def test_list_to_1d_numpy(y, dtype):
    if isinstance(y, np.ndarray) and len(y.shape) == 2:
        with pytest.warns(UserWarning, match='column-vector'):
            lgb.basic.list_to_1d_numpy(y)
        return
    elif isinstance(y, list) and isinstance(y[0], list):
        with pytest.raises(TypeError):
            lgb.basic.list_to_1d_numpy(y)
        return
    elif isinstance(y, pd_Series) and y.dtype == object:
        with pytest.raises(ValueError):
            lgb.basic.list_to_1d_numpy(y)
        return
    result = lgb.basic.list_to_1d_numpy(y, dtype=dtype)
    assert result.size == 10
    assert result.dtype == dtype

Reproducible example

pytest tests/python_package_test

Environment info

LightGBM version or commit hash:
3.2.1.99

Command(s) you used to install LightGBM

# install the Python package
git submodule init
git submodule update --recursive
cd python-package
python setup.py install

[jmoralez]

Thanks for raising this, that's definitely my bad. Will open a PR with a fix.

[github-actions]

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