mocking multiprocess pool for unittest

mock_multiprocess_pool.md

Mocking multiprocess pool apply_async method

It seems python multiprocessing interface relies on pickling, and mock library and pickling don't go well together.

write mock of multiprocess class for pytest

module code

pool = Pool(cpu_count())
pool.apply_async(func=myfunc)

Pytest

reference:

• https://stackoverflow.com/questions/26094560/python-class-inheriting-multiprocessing-mocking-one-of-the-class-objects
• https://stackoverflow.com/questions/33128681/how-to-unit-test-code-that-uses-python-multiprocessing

from unittest.mock import patch
from pytest import fixture

class MockPoolApplyResult:
    def __init__(self, func, args):
        self._func = func
        self._args = args

    def get(self, timeout=0):
        return self._func(*self._args)


@fixture(autouse=True)
def mock_pool_apply_async(monkeypatch):
    monkeypatch.setattr("multiprocessing.pool.Pool.apply_async",
                        lambda self, func, args=(), kwds={}, callback=None, error_callback=None:
                        MockPoolApplyResult(func, args))
    
class TestClass:
  def test_method():
    ...