pytest：使用夹具与 pandas dataframe 进行参数化

Question

I have a fixture, which returns a pd.DataFrame . I need to insert the individual columns ( pd.Series ) into a unit test and I would like to use parametrize .

Here's a toy example without parametrize . Every column of the dataframe will be tested individually. However, I guess I can get rid of the input_series fixture, can't I? With this code, only 1 test will be executed. However, I am looking for 3 tests while getting rid of the for-loop at the same time.

import numpy as np
import pandas as pd
import pytest


@pytest.fixture(scope="module")
def input_df():
    return pd.DataFrame(
        data=np.random.randint(1, 10, (5, 3)), columns=["col1", "col2", "col3"]
    )


@pytest.fixture(scope="module")
def input_series(input_df):
    return [input_df[series] for series in input_df.columns]


def test_individual_column(input_series):
    for series in input_series:
        assert len(series) == 5

I am basically looking for something like this:

@pytest.mark.parametrize("series", individual_series_from_input_df)
def test_individual_column(series):
    assert len(series) == 5

Answer 1

If you try to generate multiple data from a fixture based on another fixture you will get the yield_fixture function has more than one 'yield' error message.

One solution is to use fixture parametrization . In your case you want to iterate by columns so the Dataframe columns are the parameters.

# test data
input_df = pd.DataFrame(
    data=np.random.randint(1, 10, (5, 3)), columns=["col1", "col2", "col3"]
)


@pytest.fixture(
    scope="module",
    params=input_df.columns,
)
def input_series(request):
    series = request.param
    yield input_df[series]


def test_individual_column(input_series):
    assert len(input_series) == 5

This will generate one test by column of the test Dataframe.

pytest test_pandas.py
# test_pandas.py::test_individual_column[col1] PASSED
# test_pandas.py::test_individual_column[col2] PASSED
# test_pandas.py::test_individual_column[col3] PASSED