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8 changes: 8 additions & 0 deletions pandas/tests/groupby/test_groupby.py
Original file line number Diff line number Diff line change
Expand Up @@ -3189,6 +3189,14 @@ def test_depr_get_group_len_1_list_likes(test_series, kwarg, value, name, warn):
tm.assert_equal(result, expected)


def test_groupby_ngroup_with_nan():
# GH#50100
df = DataFrame({"a": Categorical([np.nan]), "b": [1]})
result = df.groupby(["a", "b"], dropna=False, observed=False).ngroup()
expected = Series([0])
tm.assert_series_equal(result, expected)


def test_get_group_axis_1():
# GH#54858
df = DataFrame(
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