如何並行執行python subTests？

Question

考慮下面的unittest.TestCase ，它實現了同一個測試的兩個版本，唯一的區別是一個使用multiprocessing並行執行subTest 。

import multiprocessing as mp
from unittest import TestCase


class TestBehaviour(TestCase):
    def _test_equals(self, val):
        for target_val in [1, 2]:
            with self.subTest(target=target_val, source=val):
                self.assertEqual(val, target_val)

    def test_equality_parallel(self):
        with mp.Pool(processes=4) as pool:
            pool.map(self._test_equals, [1, 2])
            pool.join()
            pool.close()

    def test_equality(self):
        for val in [1, 2]:
            self._test_equals(val)

串行版本test_equality按預期工作並產生以下測試失敗：

======================================================================
FAIL: test_equality (temp.TestBehaviour) (target=2, source=1)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "temp.py", line 11, in _test_equals
    self.assertEqual(val, target_val)
AssertionError: 1 != 2

======================================================================
FAIL: test_equality (temp.TestBehaviour) (target=1, source=2)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "temp.py", line 11, in _test_equals
    self.assertEqual(val, target_val)
AssertionError: 2 != 1

另一方面， test_equality_parallel會導致錯誤，因為TestCase不能被pickle：

Traceback (most recent call last):
  File "temp.py", line 15, in test_equality_parallel
    pool.map(self._test_equals, [1, 2])
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/pool.py", line 364, in map
    return self._map_async(func, iterable, mapstar, chunksize).get()
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/pool.py", line 768, in get
    raise self._value
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/pool.py", line 537, in _handle_tasks
    put(task)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/connection.py", line 206, in send
    self._send_bytes(_ForkingPickler.dumps(obj))
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/reduction.py", line 51, in dumps
    cls(buf, protocol).dump(obj)
TypeError: cannot pickle '_io.TextIOWrapper' object

現在我知道我可以將_test_equals拆分為類之外的獨立函數； 但是，我想保留subTest的行為，以便更好地記錄（和后續調試）測試失敗。

如何並行運行測試，但保留此subTest功能？

更新

我也嘗試過使用pathos.multiprocessing.ProcessingPool來規避TestCase序列化的問題； 然而，在這種情況下pool.join()引發ValueError: Pool is still running 。

from pathos.multiprocessing import ProcessingPool
...
    def test_equality_parallel(self):                                           
        pool = ProcessingPool(processes=4)                                      
        pool.map(self._test_equals, [1, 2])
        pool.join()

更新 2

這個問題肯定是相關的。 提出的第一個解決方案，為要從子進程調用的方法創建第二個類是不合適的，因為它不能使用subTest 。 第二個，從TestCase刪除 unpickleable _Outcome對象似乎很subTests ，並且考慮到子進程正在運行subTests ，看起來也不合適。

Answer 1

我是pathos （以及dill和multiprocess ）作者。 您仍然看到跨進程的pathos序列化錯誤。 您可以嘗試跨線程序列化。 線程並行可能適合這種級別的功能。

import multiprocess.dummy as mp
from unittest import TestCase


class TestBehaviour(TestCase):
    def _test_equals(self, val):
        for target_val in [1, 2]:
            with self.subTest(target=target_val, source=val):
                self.assertEqual(val, target_val)

    def test_equality_parallel(self):
        with mp.Pool(processes=4) as pool:
            pool.map(self._test_equals, [1, 2])
            pool.join()
            pool.close()

    def test_equality(self):
        for val in [1, 2]:
            self._test_equals(val)

其中產生：

======================================================================
FAIL: test_equality (test_equaltiy.TestBehaviour)
----------------------------------------------------------------------
...[snip]...
AssertionError: 1 != 2

======================================================================
FAIL: test_equality_parallel (test_equaltiy.TestBehaviour)
----------------------------------------------------------------------
...[snip]...
AssertionError: 1 != 2

----------------------------------------------------------------------
Ran 2 tests in 0.108s

FAILED (failures=2)

這告訴我您可以使用dill的序列化變體（即在dill.settings ）來解決序列化問題。 請參閱： https : //github.com/uqfoundation/multiprocess/issues/48 。