Django @override_settings does not allow dictionary?

You should override the whole dict:

@override_settings(SETTING_DICT={'key': True})
def test_something(self):
   ...

Or, you can use override_settings as a context manager:

def test_something(self):
     value = settings.SETTING_DICT
     value['key'] = True
     with override_settings(SETTING_DICT=value):
         ...

Since Python 3.3, you may use collections.Chainmap if you wand to override specific values in the dict (or other mapping) object using decorator and keep code clean from context manager. https://docs.python.org/3/library/collections.html#collections.ChainMap

from collections import ChainMap

@override_settings(SETTING_DICT=ChainMap({'key': 'value'}, settings.SETTING_DICT))
def test_something(self):
   ...

The above will not override whole dict, and all other values in SETTINGS_DICT will be available.

For Python 2.7 you may use backport, which contains Chainmap implementation. https://pypi.org/project/chainmap/

I didn't want to override the whole dict either, so I copied the dictionary in question from the settings object and just modified the attribute I was interested in:

import copy
from django.conf import settings
                                                                                                                                                     
settings_dict = copy.deepcopy(settings.SETTINGS_DICT)
settings_dict['key1']['key2'] = 'new value'

@override_settings(SETTINGS_DICT=settings_dict)
def test_something(self):
    pass

It suits my purposes, but if you wanted to make this more widely usable, you could write a short function with a few arguments which could do something like this dynamically.

Note: I tried using settings.SETTINGS_DICT.copy() instead of copy.deepcopy(settings.SETTINGS_DICT) but that seemed to globally override the setting for all tests.