import pytest

import numpy as np
import pandas as pd


# This would be added to conftest.py
@pytest.fixture(autouse=True)
def stop_chaining():
    pd.set_option("chained_assignment", "raise")


class TestExample(object):

    def test_should_fail(self):

        df = pd.DataFrame(
                {'a' : ['one', 'one', 'two', 'three',
                        'two', 'one', 'six'],
                 'c' : np.arange(7)
                }
        )

        # Chained assignment, should raise.
        df['c'][df.a.str.startswith('o')] = 42