Question

避免对会话范围内的固定装置返回的对象产生副作用的最佳方法是什么？

我的诀窍是将一个会话范围的治具和一个功能范围的治具包装在一起，该功能返回一个原始对象的副本。 PyTest中有内置的吗？可能有装饰师吗？

import pytest
from pandas import read_csv

@pytest.fixture(scope='session')
def _input_df():
    """Computationally expensive fixture, so runs once per test session.
    As an example we read in a CSV file 5000 rows, 26 columns into a pandas.DataFrame
    """
    df = read_csv('large-file.csv')

    return df


@pytest.fixture(scope='function')
def input_df(_input_df):
    """"This is a function-scoped fixture, which wraps around the session-scoped one
    to make a copy of its result."""
    return _input_df.copy()


def test_df_1(input_df):
    """Inadvertently, this test mutates the object from the input_df fixture"""
    # adding a new column
    input_df['newcol'] = 0
    # we now have 27 columns
    assert input_df.shape == (5000, 27)


def test_df_2(input_df):
    """But since we are getting a copy or the original this test still passes"""
    assert input_df.shape == (5000, 26)

Answer 1

您应该从input_df固定装置中返回复制功能对象，而无需实例化它：

import pytest
from pandas import read_csv

@pytest.fixture(scope='session')
def _input_df():
    """Computationally expensive fixture, so runs once per test session.
    As an example we read in a CSV file 5000 rows, 26 columns into a pandas.DataFrame
    """
    df = read_csv('large-file.csv')

    return df


@pytest.fixture(scope='function')
def input_df(_input_df):
    """"This is a function-scoped fixture, which wraps around the session-scoped one
    to make a copy of its result."""
    return _input_df.copy


def test_df_1(input_df):
    """Inadvertently, this test mutates the object from the input_df fixture"""
    # adding a new column
    input_df()['newcol'] = 0
    # we now have 27 columns
    assert input_df().shape == (5000, 27)


def test_df_2(input_df):
    """But since we are getting a copy or the original this test still passes"""
    assert input_df().shape == (5000, 26)

此代码示例在我的机器上运行。在这种情况下，test_df_2测试失败。

如何避免从PyTest中的会话范围固定装置中更改对象？

1 个答案: