Unit testing __main__.py

Question

I have a Python package (Python 3.6, if it makes a difference) that I've designed to run as 'python -m package arguments ' and I'd like to write unit tests for the __main__.py module. I specifically want to verify that it sets the exit code correctly. Is it possible to use runpy.run_module to execute my __main__.py and test the exit code? If so, how do I retrieve the exit code?

To be more clear, my __main__.py module is very simple. It just calls a function that has been extensively unit tested. But when I originally wrote __main__.py, I forgot to pass the result of that function to exit(), so I would like unit tests where the main function is mocked to make sure the exit code is set correctly. My unit test would look something like:

@patch('my_module.__main__.my_main', return_value=2)
def test_rc2(self, _):
    """Test that rc 2 is the exit code."""
    sys.argv = ['arg0', 'arg1', 'arg2', …]
    runpy.run_module('my_module')
    self.assertEqual(mod_rc, 2)

My question is, how would I get what I've written here as 'mod_rc'?

Thanks.

Answer 1

I have a Python package (Python 3.6, if it makes a difference) that I've designed to run as 'python -m package arguments ' and I'd like to write unit tests for the __main__.py module. I specifically want to verify that it sets the exit code correctly. Is it possible to use runpy.run_module to execute my __main__.py and test the exit code? If so, how do I retrieve the exit code?

To be more clear, my __main__.py module is very simple. It just calls a function that has been extensively unit tested. But when I originally wrote __main__.py, I forgot to pass the result of that function to exit(), so I would like unit tests where the main function is mocked to make sure the exit code is set correctly. My unit test would look something like:

@patch('my_module.__main__.my_main', return_value=2)
def test_rc2(self, _):
    """Test that rc 2 is the exit code."""
    sys.argv = ['arg0', 'arg1', 'arg2', …]
    runpy.run_module('my_module')
    self.assertEqual(mod_rc, 2)

My question is, how would I get what I've written here as 'mod_rc'?

Thanks.

Answer 2

I have a Python package (Python 3.6, if it makes a difference) that I've designed to run as 'python -m package arguments ' and I'd like to write unit tests for the __main__.py module. I specifically want to verify that it sets the exit code correctly. Is it possible to use runpy.run_module to execute my __main__.py and test the exit code? If so, how do I retrieve the exit code?

To be more clear, my __main__.py module is very simple. It just calls a function that has been extensively unit tested. But when I originally wrote __main__.py, I forgot to pass the result of that function to exit(), so I would like unit tests where the main function is mocked to make sure the exit code is set correctly. My unit test would look something like:

@patch('my_module.__main__.my_main', return_value=2)
def test_rc2(self, _):
    """Test that rc 2 is the exit code."""
    sys.argv = ['arg0', 'arg1', 'arg2', …]
    runpy.run_module('my_module')
    self.assertEqual(mod_rc, 2)

My question is, how would I get what I've written here as 'mod_rc'?

Thanks.

Answer 3

__main__.py is still subject to normal __main__ global behavior — which is to say, you can implement your __main__.py like so

def main():
  # Your stuff

if __name__ == "__main__":
  main()

and then you can test your __main__ in whatever testing framework you like by using

from your_package.__main__ import main

As an aside, if you are using argparse , you will probably want:

def main(arg_strings=None):
  # …
  args = parser.parse_args(arg_strings)
  # …

if __name__ == "__main__":
  main()

and then you can override arg strings from a unit test simply with

from your_package.__main__ import main

def test_main():
  assert main(["x", "y", "z"]) == …

or similar idiom in you testing framework.