如何在 pytest 中两次使用参数化的依赖夹具？答案

【问题标题】：How can I use a parametrized dependent fixture twice in pytest?如何在 pytest 中两次使用参数化的依赖夹具？
【发布时间】：2019-05-31 08:32:21
【问题描述】：

我试图在一次测试中多次使用参数化夹具，目的是获得所有值的笛卡尔积。

https://stackoverflow.com/a/39444098/102441 展示了如何为一个简单的夹具执行此操作：

import pytest

@pytest.fixture(params=[0, 1, 2])
def first(request):
    return request.param

second = first

# runs 3x3 = 9 times
def test_double_fixture(first, second):
    assert False, '{} {}'.format(first, second)

但是，如果参数化来自依赖的夹具，这种方法就会失败：

import pytest

@pytest.fixture(params=[0, 1, 2])
def integer(request):
    return request.param

@pytest.fixture
def squared_integer(integer):
    return integer * integer

@pytest.fixture
def first(squared_integer):
    return squared_integer

second = first

# runs only 3 times
def test_double_fixture(first, second):
    assert False, '{} {}'.format(first, second)

我怎样才能像简单示例那样运行 3x3 测试？

【问题讨论】：

标签： python pytest fixtures

【解决方案1】：

这是 pytest 的正确行为。因为您在其他灯具内部使用integer。要了解会发生什么，请使用 --setup-show 标志检查 pytest。你会看到类似的东西：

        SETUP    F integer[0]
        SETUP    F squared_integer (fixtures used: integer)
        SETUP    F first (fixtures used: squared_integer)
        SETUP    F second (fixtures used: squared_integer)
        Test/test_54044536_3.py::test_double_fixture[0] (fixtures used: first, integer, second, squared_integer)F
        TEARDOWN F second
        TEARDOWN F first
        TEARDOWN F squared_integer
        TEARDOWN F integer[0]

因此整数值仅适用于 squared_integer 函数。

为了回答您的问题，我们可以将您的代码重构为固定装置和一个函数。这看起来像：

import pytest

def squared_integer(integer):
    return integer * integer


@pytest.fixture(params=[0, 1, 2])
def first(request):
    return squared_integer(request.param)

second = first

# runs only 3 times
def test_double_fixture(first, second):
    assert False, '{} {}'.format(first, second)

您将有 9 个具有这样顺序的测试：

        SETUP    F first[0]
        SETUP    F second[0]
        Test/test_54044536_2.py::test_double_fixture[0-0] (fixtures used: first, second)F
        TEARDOWN F second[0]
        TEARDOWN F first[0]
        SETUP    F first[0]
        SETUP    F second[1]
        Test/test_54044536_2.py::test_double_fixture[0-1] (fixtures used: first, second)F
        TEARDOWN F second[1]
        TEARDOWN F first[0]
        SETUP    F first[0]
        SETUP    F second[2]
        Test/test_54044536_2.py::test_double_fixture[0-2] (fixtures used: first, second)F
        TEARDOWN F second[2]
        TEARDOWN F first[0]
        SETUP    F first[1]
        SETUP    F second[0]
        Test/test_54044536_2.py::test_double_fixture[1-0] (fixtures used: first, second)F
        TEARDOWN F second[0]
        TEARDOWN F first[1]
        SETUP    F first[1]
        SETUP    F second[1]
        Test/test_54044536_2.py::test_double_fixture[1-1] (fixtures used: first, second)F
        TEARDOWN F second[1]
        TEARDOWN F first[1]
        SETUP    F first[1]
        SETUP    F second[2]
        Test/test_54044536_2.py::test_double_fixture[1-2] (fixtures used: first, second)F
        TEARDOWN F second[2]
        TEARDOWN F first[1]
        SETUP    F first[2]
        SETUP    F second[0]
        Test/test_54044536_2.py::test_double_fixture[2-0] (fixtures used: first, second)F
        TEARDOWN F second[0]
        TEARDOWN F first[2]
        SETUP    F first[2]
        SETUP    F second[1]
        Test/test_54044536_2.py::test_double_fixture[2-1] (fixtures used: first, second)F
        TEARDOWN F second[1]
        TEARDOWN F first[2]
        SETUP    F first[2]
        SETUP    F second[2]
        Test/test_54044536_2.py::test_double_fixture[2-2] (fixtures used: first, second)F
        TEARDOWN F second[2]
        TEARDOWN F first[2]

【讨论】：

【解决方案2】：

如果您对顶层夹具的副本没有问题（在这种情况下 squared_integer 的化身为 first 和 second），您也可以复制低层夹具并将其用作另一个输入一级：

import pytest

@pytest.fixture(params=[0, 1, 2])
def integer(request):
    return request.param
integer2 = integer

@pytest.fixture
def squared_integer(integer, integer2):
    return integer * integer2
second = first = squared_integer

# runs 9 times
def test_double_fixture_lowlevel(integer, integer2):
    assert False, '{} {}'.format(integer, integer2)

# also runs 9 times
def test_double_fixture_toplevel(first, second):
    assert False, '{} {}'.format(first, second)

【讨论】：