Question

What I want to do

I’m trying to write unit test to check that my regexp is constructed properly:

# mediamanager/models.py

import re

from django.conf import settings

filetypes_re = {}
for key, exts in settings.MM_FILETYPES.items():
    filetypes_re[key] = re.compile(r'({})'.format('|'.join(exts)))

NOTE: Actually, I’m not sure why I’m writing this unittest at all, since this piece of code is more than straighforward… But that’s not the point.

As you can see, the final regexp depends on variable settings.MM_FILETYPES which can be set by user. I need to test specific input and for this case, Django provides decorator @override_settings which temporary overrides settings values:

# mediamanager/tests.py

import unittest
from django.test.utils import override_settings
from mediamanager.models import (filetypes_re, …)  # import everything we want to test

class ModelsTestCase(unittest.TestCase):
    @override_settings(MM_FILETYPES={'image': ['jpg', 'png', 'gif'],
                                     'document': ['pdf', 'txt'],
                                     'audio': ['mp3', 'wav']})
    def test_filetype_re(self):
        filetypes_re_exp = {'image': '(jpg|png|gif)',
                            'document': '(pdf|txt)',
                            'audio': '(mp3|wav)'}

        for key, value in filetypes_re_exp.items():
            self.assertEqual(value, filetypes_re[key].pattern)

This test unfortunatelly don’t pass. Module mediamanager.models is loaded before the settings are overriden and therefore the filetypes_re is compiled using old settings. I need to reload it (somehow) to new settings take effect.

Problem

I altered unittest in this way:

@override_settings(MM_FILETYPES={'image': ['jpg', 'png', 'gif'],
                                 'document': ['pdf', 'txt'],
                                 'audio': ['mp3', 'wav']})
def test_filetype_re(self):
    import mediamanager.models  # obtaining module object from sys.modules have the same result
    reload(mediamanager.models)
    filetypes_re = mediamanager.models.filetypes_re
    filetypes_re_exp = {'image': '(jpg|png|gif)',
                        'document': '(pdf|txt)',
                        'audio': '(mp3|wav)'}

    for key, value in filetypes_re_exp.items():
        self.assertEqual(value, filetypes_re[key].pattern)

And test passed. But probably because I imported other objects from mediamanager.models module, other tests in this test case failed. Not all of them, only two (which is strange). EDIT: It’s not strange at all. Only fails tests which runs after test_filetyes_re and reload() call.

Questions

How to ‘reload’ module mediamanager.models in a way that:

1. filetypes_re are evaluated with new settings?
2. All other objects imported from same model remains unaffected?

Should I rewrite a piece of code only because it became unstable after reload (I mean other those objects from mediamanager.models which don’t pass test after reload)? I’ve read some articles about reloading modules that usually it’s not a good idea.

Is there a better way to define module level objects, like this regexp, to make testing easier?

Answer 1

there are a couple of ways. off the top of my head:

# mediamanager/models.py

import re

from django.conf import settings

def get_filetypes_re(mm_filetypes=settings.MM_FILETYPES):
    filetypes_re = {}
    for key, exts in settings.MM_FILETYPES.items():
    filetypes_re[key] = re.compile(r'({})'.format('|'.join(exts)))
    return filetypes_re 

and your test:

MM_FILETYPES={'image': ['jpg', 'png', 'gif'],
                        'document': ['pdf', 'txt'],
                        'audio': ['mp3', 'wav']})

def test_filetype_re(self):
    filetypes_re = mediamanager.models.get_filetypes_re(mm_filetypes=MM_FILETYPES)
    filetypes_re_exp = {'image': '(jpg|png|gif)',
                        'document': '(pdf|txt)',
                        'audio': '(mp3|wav)'}

    for key, value in filetypes_re_exp.items():
        self.assertEqual(value, filetypes_re[key].pattern)