Using Mock.side_effect for an instance method

Question

I am trying to mock an instance method in Python with a side_effect. I want/expect my side effect to be called with an initial 'self' argument that I can use to determine the return value.

So I have something like this:

import mock

class TestCases(unittest.TestCase):

  @mock.patch('Item.exists')
  def test_foo(self, mock_item_exists):

    def item_exists_side_effect(*args, **kwargs):
      # I expect args[0] here to be supplied and to refer to the item
      _self = args[0]
      return _self.name == 'bar'

    mock_item_exists.side_effect = item_exists_side_effect

    ...

However, when Item.exists() gets called I end up in my side-effect function but with an empty args list.

Is this expected? Am I doing something wrong?

Answer 1

Looks like this is the reason:

Why does mock ignore the instance/object passed to a mocked out method when it is called?

Ie by calling mock.patch I turned the instance method into a class method.