py.test：如何在子进程中自动检测异常？

Question

我正在大量使用多处理的模块环境中在Linux上运行py.test。子进程中的异常不会检测为错误。测试文件示例pytest_mp_test.py：

import multiprocessing

def test_mp():
    p = multiprocessing.Process(target=child)
    p.start()
    p.join()

def child():
    assert False

执行：

$ py.test pytest_mp_test.py 
================================== test session starts ===================================
platform linux2 -- Python 2.7.3 -- pytest-2.3.3
plugins: cov
collected 1 items 

pytest_mp_test.py .

================================ 1 passed in 0.04 seconds ================================

未检测到错误。使用以下命令调用时将打印异常-s：

$ py.test -s pytest_mp_test.py 
================================== test session starts ===================================
platform linux2 -- Python 2.7.3 -- pytest-2.3.3
plugins: cov
collected 1 items 

pytest_mp_test.py Process Process-1:
Traceback (most recent call last):
  File "/apps11/bioinfp/Python-2.7.3/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/apps11/bioinfp/Python-2.7.3/lib/python2.7/multiprocessing/process.py", line 114, in run
    self._target(*self._args, **self._kwargs)
  File "/home/bioinfp/jang/hobbyproggorn/gevent-messagepipe/gevent-messagepipe/pytest_mp_test.py", line 9, in child
    assert False
AssertionError: assert False
.

================================ 1 passed in 0.04 seconds ================================

当我手动查看测试日志时，我意识到有问题。但是，我想知道是否有一种巧妙的方法可以在带有py.test的孩子中自动进行异常检测。

我必须在父母中验证孩子的退出代码吗？这是唯一的方法吗？

Answer 1

经过进一步考虑，我认为仅在子进程中捕获预期的异常并检查子进程的退出状态是一种非常干净可靠的解决方案，不会在测试中添加其他IPC组件。示例代码：

import multiprocessing
from py.test import raises

class CustomError(Exception):
    pass

def test_mp_expected_fail():
    p = multiprocessing.Process(target=child_expected_fail)
    p.start()
    p.join()
    assert not p.exitcode

def test_mp_success():
    p = multiprocessing.Process(target=child)
    p.start()
    p.join()
    assert not p.exitcode

def test_mp_unexpected_fail():
    p = multiprocessing.Process(target=child_unexpected_fail)
    p.start()
    p.join()
    assert not p.exitcode


def child_expected_fail():
    with raises(CustomError):
        raise CustomError

def child_unexpected_fail():
    raise TypeError

def child():
    pass

执行：

$ py.test pytest_mp_test.py 
================================== test session starts ===================================
platform linux2 -- Python 2.7.3 -- pytest-2.3.3
plugins: cov
collected 3 items 

pytest_mp_test.py ..F

======================================== FAILURES ========================================
________________________________ test_mp_unexpected_fail _________________________________

    def test_mp_unexpected_fail():
        p = multiprocessing.Process(target=child_unexpected_fail)
        p.start()
        p.join()
>       assert not p.exitcode
E       assert not 1
E        +  where 1 = <Process(Process-3, stopped[1])>.exitcode

pytest_mp_test.py:23: AssertionError
------------------------------------ Captured stderr -------------------------------------
Process Process-3:
Traceback (most recent call last):
  File "/apps11/bioinfp/Python-2.7.3/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/apps11/bioinfp/Python-2.7.3/lib/python2.7/multiprocessing/process.py", line 114, in run
    self._target(*self._args, **self._kwargs)
  File "/home/bioinfp/jang/hobbyproggorn/gevent-messagepipe/gevent-messagepipe/pytest_mp_test.py", line 31, in child_unexpected_fail
    raise TypeError
TypeError
=========================== 1 failed, 2 passed in 0.07 seconds ===========================