python - 过滤 pytest 固定装置

Question

这与 older question 基本相同但希望现在有更好的解决方案。
问题 :给定一个参数化的 fixture ，如何使用 fixture 对象的子集参数化测试功能？
示例 :

import pytest

@pytest.fixture(params=range(7))
def square(request):
    return request.param ** 2

def test_all_squares(square):
    sqrt = square ** 0.5
    assert sqrt == int(sqrt)

@pytest.fixture()
def odd_square(square):
    if square % 2 == 1:
        return square
    pytest.skip()

def test_all_odd_squares(odd_square):
    assert odd_square % 2 == 1
    sqrt = odd_square ** 0.5
    assert sqrt == int(sqrt)

输出 :

$ pytest pytests.py  -v=================================================================== test session starts ===================================================================...collected 14 items                                                                                                                                        pytests.py::test_all_squares[0] PASSED                                                                                                              [  7%]pytests.py::test_all_squares[1] PASSED                                                                                                              [ 14%]pytests.py::test_all_squares[2] PASSED                                                                                                              [ 21%]pytests.py::test_all_squares[3] PASSED                                                                                                              [ 28%]pytests.py::test_all_squares[4] PASSED                                                                                                              [ 35%]pytests.py::test_all_squares[5] PASSED                                                                                                              [ 42%]pytests.py::test_all_squares[6] PASSED                                                                                                              [ 50%]pytests.py::test_all_odd_squares[0] SKIPPED                                                                                                         [ 57%]pytests.py::test_all_odd_squares[1] PASSED                                                                                                          [ 64%]pytests.py::test_all_odd_squares[2] SKIPPED                                                                                                         [ 71%]pytests.py::test_all_odd_squares[3] PASSED                                                                                                          [ 78%]pytests.py::test_all_odd_squares[4] SKIPPED                                                                                                         [ 85%]pytests.py::test_all_odd_squares[5] PASSED                                                                                                          [ 92%]pytests.py::test_all_odd_squares[6] SKIPPED                                                                                                         [100%]============================================================== 10 passed, 4 skipped in 0.02s ==============================================================

Although this works, it's not ideal:

• It creates dummy test cases that are always skipped
• It requires test functions that use the filtered fixture to give a different name (odd_square) to the parameter.

What I'd like instead is e.g. a filter_fixture(predicate, fixture) function that filters the original fixture's objects and can be passed to pytest.mark.parametrize, something like this:

@pytest.mark.parametrize("square", filter_fixture(lambda x: x % 2 == 1, square))
def test_all_odd_squares(square):
    assert square % 2 == 1
    sqrt = square ** 0.5
    assert sqrt == int(sqrt)

这在某种程度上可行吗？

Answer 1

如果您需要一定程度的逻辑来确定将哪些参数应用于每个测试，您可能需要考虑使用 pytest_generate_tests hook.
钩子(Hook)函数pytest_generate_tests为每个收集的测试调用。 metafunc参数允许您动态参数化每个单独的测试用例。重写您的示例以使用 pytest_generate_tests可能看起来像这样:

def pytest_generate_tests(metafunc):
    square_parameters = (x**2 for x in range(7))
    if 'square' in metafunc.fixturenames:
        metafunc.parametrize("square", square_parameters)
    if 'odd_square' in metafunc.fixturenames:
        odd_square_parameters = (x for x in square_parameters if x % 2 == 1)
        metafunc.parametrize("odd_square", odd_square_parameters)

def test_all_squares(square):
    sqrt = square ** 0.5
    assert sqrt == int(sqrt)

def test_all_odd_squares(odd_square):
    assert odd_square % 2 == 1
    sqrt = odd_square ** 0.5
    assert sqrt == int(sqrt)

这将导致运行以下测试用例:

$ pytest -v pytests.py 
=========== test session starts ===========
…
collected 10 items

pytests.py::test_all_squares[0] PASSED                                                                                                                                                                                     [ 10%]
pytests.py::test_all_squares[1] PASSED                                                                                                                                                                                     [ 20%]
pytests.py::test_all_squares[4] PASSED                                                                                                                                                                                     [ 30%]
pytests.py::test_all_squares[9] PASSED                                                                                                                                                                                     [ 40%]
pytests.py::test_all_squares[16] PASSED                                                                                                                                                                                    [ 50%]
pytests.py::test_all_squares[25] PASSED                                                                                                                                                                                    [ 60%]
pytests.py::test_all_squares[36] PASSED                                                                                                                                                                                    [ 70%]
pytests.py::test_all_odd_squares[1] PASSED                                                                                                                                                                                 [ 80%]
pytests.py::test_all_odd_squares[9] PASSED                                                                                                                                                                                 [ 90%]
pytests.py::test_all_odd_squares[25] PASSED                                                                                                                                                                                [100%]

=========== 10 passed in 0.03s ===========

请注意，我的示例中的测试 ID 与您的略有不同。但是，您可以使用 ìds 提供明确的测试标识符。 metafunc.parametrize 的论点.