Executing Python tests that use multiprocessing module in Windows

app.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from multiprocessing import Pool

def f(x):
    return x*x

def run():
    pool = Pool(processes=4)              # start 4 worker processes
    print pool.map(f, range(10))          # prints "[0, 1, 4,..., 81]"
    return 0

if __name__ == '__main__':
    exit(run())

Executing Python unittest

C:\multiprocessing_unittest>python -m unittest discover
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
.
----------------------------------------------------------------------
Ran 1 test in 0.219s

OK

test.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import unittest
import app
import sys

class TestExtractReturnsDataset(unittest.TestCase):

    def test(self):

        # Very dirty hack
        # To fix the Windows forking system it's necessary to point __main__ to
        # the module we want to execute in the forked process
        old_main =                          sys.modules["__main__"]
        old_main_file =                     sys.modules["__main__"].__file__
        sys.modules["__main__"] =           sys.modules["app"]
        sys.modules["__main__"].__file__ =  sys.modules["app"].__file__

        result = app.run()

        sys.modules["__main__"] =           old_main
        sys.modules["__main__"].__file__ =  old_main_file

        self.assertEqual(result, 0)