python runtime_error ai_generated true

FAILED tests/test_b.py::test_uses_cache - KeyError: 'user:42' # passes when run alone: pytest tests/test_b.py::test_uses_cache

ID: python/pytest-flaky-ordering-dependency

Also available as: JSON · Markdown · 中文
80%Fix Rate
87%Confidence
0Evidence
2024-07-30First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
7.x active — — —
8.x active — — —

Root Cause

test_b relies on state written by test_a (module-level cache, global, or shared DB row) and pytest's default ordering runs them in file order; running in isolation or with -p randomly changes order.

generic

中文

test_b 依赖 test_a 写入的状态（模块级缓存、全局变量或共享数据库行），pytest 默认按文件顺序运行；单独运行或使用 -p 随机排序会改变顺序。

Workarounds

  1. 95% success 
    @pytest.fixture
def seeded_cache(cache):
    cache['user:42'] = {'name': 'Alice'}
    return cache

def test_uses_cache(seeded_cache):
    assert seeded_cache['user:42']['name'] == 'Alice'
  2. 85% success 
    # pyproject.toml
[tool.pytest.ini_options]
addopts = "-p no:randomly"  # only in local dev

# CI:
pytest -p randomly --randomly-seed=random -x
# Then refactor tests that fail only under reordering

Dead Ends

Common approaches that don't work:

  1. 80% fail

    A fixed seed gives the same order locally but CI may use a different seed; the inter-test dependency remains a latent bug.

  2. 75% fail

    Couples tests by name and breaks under -p no:randomly or when parallelized with xdist.