python - 为什么 `py.test --last-failed` 会跳过许多测试，尽管之前没有测试失败？

Question

突然 py.test --last-failed 跳过了很多测试，尽管在之前的测试运行中没有测试失败。以下是首先运行 py.test --vv ，然后运行 ​​py.test --vv --last-failed 的输出:

$venv/bin/py.test -vv
======================================================================= test session starts =======================================================================
platform darwin -- Python 3.7.3, pytest-4.6.3, py-1.8.0, pluggy-0.12.0 -- /Users/lars/coding/talea/fahrtwind/products/backend/venv/bin/python3
cachedir: .pytest_cache
rootdir: /Users/lars/coding/talea/fahrtwind/products/backend, inifile: pytest.ini, testpaths: tests
plugins: forked-1.0.2, env-0.6.2, xdist-1.28.0, cov-2.7.1
collected 888 items
...                                                                                                                                     
<HERE ALL 888 TESTS ARE RUN AND ALL PASS>
...
=================================================================== 888 passed in 63.89 seconds ===================================================================
$
$
$venv/bin/py.test -vv --last-failed
======================================================================= test session starts =======================================================================
platform darwin -- Python 3.7.3, pytest-4.6.3, py-1.8.0, pluggy-0.12.0 -- /Users/lars/coding/talea/fahrtwind/products/backend/venv/bin/python3
cachedir: .pytest_cache
rootdir: /Users/lars/coding/talea/fahrtwind/products/backend, inifile: pytest.ini, testpaths: tests
plugins: forked-1.0.2, env-0.6.2, xdist-1.28.0, cov-2.7.1
collected 303 items                                                                                                                                               
run-last-failure: 181 known failures not in selected tests (skipped 206 files)
...
<HERE ONLY 303 TESTS ARE RUN>
...

为什么py.test --last-failed会跳过许多测试，尽管之前没有测试失败？

Answer 1

正如评论中所建议的，使缓存无效是解决方案:要么通过重新运行测试

$ pytest --cache-clear

或者，如果测试套件需要很长时间才能重新运行，只需删除项目根目录中的 .pytest_cache 目录(对于旧版本的pytest)。另外，引用 Clearing Cache content部分:

You can instruct pytest to clear all cache files and values by adding the --cache-clear option like this:

pytest --cache-clear

This is recommended for invocations from Continuous Integration servers where isolation and correctness is more important than speed.

因此，指示 CI 服务器在每次运行时使缓存失效是一个很好的做法，这样您在遇到由于本地缓存导致的意外故障时就有引用。