如何在python中编写多线程代码的单元测试

Question

假设我有一些python模块（application.py），它包含一些复杂的业务逻辑，并启用了多线程或多进程。例如，

application.py

from multiprocessing.pool import ThreadPool

class application:

    def __init__(service):
        self.service = service

    def execute():
        pool = ThreadPool(processes=2)
        task1 = pool.apply_async(service.get, "1")
        task2 = pool.apply_async(service.get, "2")
        if task1.successful() and task2.successful():
            return True

test_application.py（我在单元测试中使用mockito库）

class test_application(Unittest.TestCase):

    def test_execute():
        service = mock()
        when(service).get(ANY()).thenReturn(200)
        fakeApplication = application(service=service)

        status = fakeApplication.execute()

        self.assertEquals(True, stautus)

如果task1.successful（）和task2.successful（）：

，我发现测试用例在行中失败了

Failure
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/case.py", line 59, in testPartExecutor
    yield
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/case.py", line 605, in run
    testMethod()
  File "/ENV/lib/python3.6/site-packages/mock/mock.py", line 1305, in patched
    return func(*args, **keywargs)
  File "TransactionTest.py", line 69, in test_create_transaction_TT
    actual = application.execute()
  File "/Transaction.py", line 45, in start_transaction
    if task1.successful() and task2.successful():
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/multiprocessing/pool.py", line 631, in successful
    assert self.ready()
AssertionError

我认为单元测试调用的execute（）方法实际上并没有创建ThreadPool功能。

一些问题：   - unittest不使用python的线程池库吗？   - 如何在不重写代码的情况下对application.py进行单元测试？   - 用于多线程测试的任何现有python模块？