How to test or mock “if __name__ == '__main__'” contents

Question

Say I have a module with the following:

def main():
    pass

if __name__ == \"__main__\":
    main()

I want to write a unit test for the b

Answer 1

Python 3 solution:

import os
from importlib.machinery import SourceFileLoader
from importlib.util import spec_from_loader, module_from_spec
from importlib import reload
from unittest import TestCase
from unittest.mock import MagicMock, patch
    

class TestIfNameEqMain(TestCase):
    def test_name_eq_main(self):
        loader = SourceFileLoader('__main__',
                                  os.path.join(os.path.dirname(os.path.dirname(__file__)),
                                               '__main__.py'))
        with self.assertRaises(SystemExit) as e:
            loader.exec_module(module_from_spec(spec_from_loader(loader.name, loader)))

Using the alternative solution of defining your own little function:

# module.py
def main():
    if __name__ == '__main__':
        return 'sweet'
    return 'child of mine'

You can test with:

# Override the `__name__` value in your module to '__main__'
with patch('module_name.__name__', '__main__'):
    import module_name
    self.assertEqual(module_name.main(), 'sweet')

with patch('module_name.__name__', 'anything else'):
    reload(module_name)
    del module_name
    import module_name
    self.assertEqual(module_name.main(), 'child of mine')