如何测试 pytest fixture 本身？

Question

测试 pytest fixture 本身的正确方法是什么。请不要将它与在测试中使用夹具混淆。我只想自己测试固定装置的正确性。

当我尝试在测试中调用并执行它们时，我面临：

Fixture "app" called directly. Fixtures are not meant to be called directly

如有任何意见，我们将不胜感激。关于这个主题的文档没有给我有意义的指导：https://docs.pytest.org/en/latest/deprecations.html#calling-fixtures-directly

测试装置本身的动力来自于我，因为当我们的测试由于装置中的错误而失败时，我们的 TAP 文件中没有正确跟踪，是什么促使我单独测试装置。

Answer 1

pytest 有一个 pytester 插件，是为了测试 pytest 本身和插件而制作的；它在不影响当前测试运行的隔离运行中执行测试。示例：

# conftest.py

import pytest

pytest_plugins = ['pytester']

@pytest.fixture
def spam(request):
    yield request.param

fixture spam 有一个问题，它只能用于参数化测试；一旦在未参数化测试中被请求，它将引发 AttributeError。这意味着我们无法通过这样的常规测试来测试它：

def test_spam_no_params(spam):
    # too late to verify anything - spam already raised in test setup!
    # In fact, the body of this test won't be executed at all.
    pass

相反，我们使用 pytester 插件提供的 testdir 夹具在隔离测试运行中执行测试：

import pathlib
import pytest


# an example on how to load the code from the actual test suite
@pytest.fixture
def read_conftest(request):
    return pathlib.Path(request.config.rootdir, 'conftest.py').read_text()


def test_spam_fixture(testdir, read_conftest):
    # you can create a test suite by providing file contents in different ways, e.g.
    testdir.makeconftest(read_conftest)
    testdir.makepyfile(
        """
        import pytest

        @pytest.mark.parametrize('spam', ('eggs', 'bacon'), indirect=True)
        def test_spam_parametrized(spam):
            assert spam in ['eggs', 'bacon']

        def test_spam_no_params(spam):
            assert True
""")
    result = testdir.runpytest()
    # we should have two passed tests and one failed (unarametrized one)
    result.assert_outcomes(passed=3, error=1)
    # if we have to, we can analyze the output made by pytest
    assert "AttributeError: 'SubRequest' object has no attribute 'param'" in ' '.join(result.outlines)

另一种为测试加载测试代码的便捷方法是 testdir.copy_example 方法。在pytest.ini中设置根路径，例如：

[pytest]
pytester_example_dir = samples_for_fixture_tests
norecursedirs = samples_for_fixture_tests

现在创建文件 samples_for_fixture_tests/test_spam_fixture/test_x.py，内容如下：

import pytest

@pytest.mark.parametrize('spam', ('eggs', 'bacon'), indirect=True)
def test_spam_parametrized(spam):
    assert spam in ['eggs', 'bacon']

def test_spam_no_params(spam):
    assert True

（与之前作为字符串传递给 testdir.makepyfile 的代码相同）。上述测试改为：

def test_spam_fixture(testdir, read_conftest):
    testdir.makeconftest(read_conftest)
    # pytest will now copy everything from samples_for_fixture_tests/test_spam_fixture
    testdir.copy_example()
    testdir.runpytest().assert_outcomes(passed=3, error=1)

这样，您就不必在测试中将 Python 代码维护为字符串，并且还可以通过运行将它们与 pytester 结合来重用现有的测试模块。也可以通过pytester_example_path标记配置测试数据根：

@pytest.mark.pytester_example_path('fizz')
def test_fizz(testdir):
    testdir.copy_example('buzz.txt')

将查找相对于项目根目录的文件 fizz/buzz.txt。

有关更多示例，请务必直接查看 Testing plugins in pytest docs; also, you may find to the question helpful as it contains yet another working example to the topic. I have also found it very helpful to study the Testdir code 部分，遗憾的是 pytest 没有为其提供详尽的文档，但代码非常多 self-documenting。

如何测试 pytest fixture 本身？

How to test the pytest fixture itself?

python

unit-testing

fixtures

pytest