venv/lib/python3.11/site-packages/pandas/tests/base/test_fillna.py

"""
Though Index.fillna and Series.fillna has separate impl,
test here to confirm these works as the same
"""

import numpy as np
import pytest

from pandas import MultiIndex
import pandas._testing as tm
from pandas.tests.base.common import allow_na_ops


def test_fillna(index_or_series_obj):
    # GH 11343
    obj = index_or_series_obj

    if isinstance(obj, MultiIndex):
        msg = "isna is not defined for MultiIndex"
        with pytest.raises(NotImplementedError, match=msg):
            obj.fillna(0)
        return

    # values will not be changed
    fill_value = obj.values[0] if len(obj) > 0 else 0
    result = obj.fillna(fill_value)

    tm.assert_equal(obj, result)

    # check shallow_copied
    assert obj is not result


@pytest.mark.parametrize("null_obj", [np.nan, None])
def test_fillna_null(null_obj, index_or_series_obj):
    # GH 11343
    obj = index_or_series_obj
    klass = type(obj)

    if not allow_na_ops(obj):
        pytest.skip(f"{klass} doesn't allow for NA operations")
    elif len(obj) < 1:
        pytest.skip("Test doesn't make sense on empty data")
    elif isinstance(obj, MultiIndex):
        pytest.skip(f"MultiIndex can't hold '{null_obj}'")

    values = obj._values
    fill_value = values[0]
    expected = values.copy()
    values[0:2] = null_obj
    expected[0:2] = fill_value

    expected = klass(expected)
    obj = klass(values)

    result = obj.fillna(fill_value)
    tm.assert_equal(result, expected)

    # check shallow_copied
    assert obj is not result