Testing module execution with pytest

Question

I have a python module that gets executed as python -m my_package.my_module --arg1 a1 --arg2 a2. Which creates an artifact on the local disk and uploads that artifact to a cloud bucket.

My module essentially looks like this

import argparse

def func():
    # parse args
    # create artifact
    # upload to bucket

func()

I'd like to write a test for this module which I can run from a different script, say test_module.py. I would like to mock the cloud api so nothing gets uploaded, but also provide a set of test command line args to the module.

So far I can do something like this

#test_module.py
from unittest import mock

def test_my_module():
    test_args = # [  test args ]
    with mock.patch.object(sys, 'argv', test_args):
        import my_package.my_module
        # test file is written to local dir

The problem here is that I can't mock the cloud api without first importing my_package.my_module which runs the code in the module and uploads the artifact. And if I do something like this

#test_module.py
from unittest import mock
import my_package.my_module

@mock.patch('my_package.my_module.cloud_client')
def test_my_module():
    # run test

Then the code will execute on the first import statement import my_package.my_module. Is there a solution where I can mock an object before importing the module it's located in?

rdas · Accepted Answer · 2020-11-12 06:03:11Z

3

Use the idiomatic solution to this exact problem:

import argparse

def func():
    # parse args
    # create artifact
    # upload to bucket

# Ensure this function only runs when this module is being executed as main, not when imported.
if __name__ == '__main__':
    func()

You can find more details here: What does if __name__ == "__main__": do?

After your module is imported (but not run) in the test, you can setup your mock & perform the test.

answered Nov 12, 2020 at 6:03

rdas

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1 Comment

mr3543 Over a year ago

Ah yes of course. Thank you. I was so convinced that running the module with the -m flag would change the __name__ variable (something I must have mistakenly thought some time ago) that I didn't even bother testing this. Thanks!

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