How to mock a dictionary in Python

For anyone coming across this later, there is also mock.patch.dict which can be used as a context manager, decorator, or class decorator.

For example:

from mock import patch

foo = {}
@patch.dict(foo, {"is_active": True})
def test():
    assert foo['is_active'] == True

Or to mock os.environ which is how I came across this question:

import os
from mock import patch

@patch.dict("os.environ", {"FOO": "BAR"})
def test_env():
    assert os.environ['FOO'] == "BAR"

How to mock a dictionary in Python is a good/direct question someone else can search, so:

1. I suggest MagicMock instead of Mock
2. Overload the __getitem__

from unittest.mock import MagicMock

m = MagicMock()
d = {'key_1': 'value'}
m.__getitem__.side_effect = d.__getitem__

# dict behaviour
m['key_1'] # => 'value'
m['key_2'] # => raise KeyError

# mock behaviour
m.foo(42)
m.foo.assert_called_once_with(43) # => raise AssertionError

Related Questions:

• How to let MagicMock behave like a dict?
• Understanding __getitem__ method

=== EDIT ===

As a function for direct copy/pasting

def mock_dict(d):
  m = MagicMock()
  m.__getitem__.side_effect = d.__getitem__
  return m

You can use this to make a mock behave like a dictionary:

mock = mocker.MagicMock()
mock.__getitem__.side_effect = lambda x: getattr(mock, x)

With that code mock['some_property'] equals to mock.some_property. This way you can still use your autogenerated Mocks so useful for assertions, which is why I didn't like the accepted answer.

If you still need to access the methods of the dictionary then the code will need further work.